Liquid crystal display device

ABSTRACT

The liquid crystal display device of the present invention includes a first substrate, a second substrate and a vertically aligned liquid crystal layer interposed between the first and second substrate. The device has a plurality of pixels each including a first electrode formed on the first substrate, a second electrode formed on the second substrate, and the liquid crystal layer interposed between the first and second electrode, and a shading region provided around the pixels. A plurality of supports for defining the thickness of the liquid crystal layer are placed regularly on the surface of the first or second substrate facing the liquid crystal layer in the shading region. The liquid crystal layer forms at least one liquid crystal domain exhibiting axisymmetric alignment when at least a predetermined voltage is applied, and the tilt direction of liquid crystal molecules in the at least one liquid crystal domain is defined with inclined sides of the plurality of supports.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device andmore particularly relates to a liquid crystal display device suitablyused for portable information terminals (for example, PDAs), mobilephones, car-mounted liquid crystal displays, digital cameras, PCs,amusement equipment, TVs and the like.

2. Description of the Related Art

The information infrastructure is advancing day to day, and equipmentsuch as mobile phones, PDAs, digital cameras, video cameras and carnavigators has penetrated deeply into people's lives. Liquid crystaldisplay (LCD) devices have been adopted in most of such equipment. Withincrease of the information amount handled with the main bodies of theequipment, LCD devices are requested to display a larger amount ofinformation, and are demanded by the market for higher contrast, a widerviewing angle, higher brightness, multiple colors and higher definition.

A vertical alignment mode using a vertically aligned liquid crystallayer has increasingly received attention as a display mode enablinghigh contrast and a wide viewing angle. The vertically aligned liquidcrystal layer is generally obtained using a vertical alignment film anda liquid crystal material having negative dielectric anisotropy.

For example, Japanese Laid-Open Patent Publication No. 6-301036(Literature 1) discloses an LCD device in which an inclined electricfield is generated around an opening formed in a counter electrode thatfaces a pixel electrode via a liquid crystal layer, so that liquidcrystal molecules surrounding liquid crystal molecules existing in theopening, which are in the vertically aligned state, are aligned ininclined directions around the opening as the center, to thereby improvethe visual angle characteristics.

However, in the device described in Literature 1, it is difficult togenerate an inclined electric field over the entire region of eachpixel. Therefore, each pixel has a region in which liquid crystalmolecules delay in response to a voltage, and this causes a problem ofoccurrence of an afterimage phenomenon.

To solve the above problem, Japanese Laid-Open Patent Publication No.2000-47217 (Literature 2) discloses an LCD device in which a pluralityof openings are provided regularly in a pixel electrode or a counterelectrode, to form a plurality of liquid crystal domains each havingaxisymmetric alignment in each pixel.

Japanese Laid-Open Patent Publication No. 2003-167253 (Literature 3)discloses a technology in which a plurality of projections are providedregularly in each pixel to stabilize the aligned state of liquid crystaldomains having radially inclined alignment formed around theprojections. This literature also discloses using an inclined electricfield generated at openings formed in an electrode, together with thealignment regulating force of the projections, to regulate the alignmentof liquid crystal molecules, and thus improve the displaycharacteristics.

Japanese Laid-Open Patent Publication No. 2001-337332 (Literature 4)discloses a multi-domain vertically aligned LCD device in which wallspacers having inclined sides are provided to define the directions oftilt of liquid crystal molecules using the alignment regulating force ofthe inclined sides. This technology eliminates the necessity ofperforming an additional step for providing an alignment regulatingstructure and also can suppress a variation in inter-substrate spacing(thickness of the liquid crystal layer) even for large-screen devices.

In recent years, a type of LCD device providing high-quality displayboth outdoors and indoors has been proposed (see Japanese Patent GazetteNo. 2955277 (Literature 5) and U.S. Pat. No. 6,195,140 (Literature 6),for example). In this type of LCD device, called a transflective LCDdevice, each pixel has a reflection region in which display is done inthe reflection mode and a transmission region in which display is donein the transmission mode.

The currently available transflective LCD devices adopt an ECB mode, aTN mode and the like. Literature 3 described above also disclosesadoption of the vertical alignment mode for, not only a transmissive LCDdevice, but also a transflective LCD device. Japanese Laid-Open PatentPublication No. 2002-350853 (Literature 7) discloses a technology inwhich in a transflective LCD device having a vertically aligned liquidcrystal layer, the alignment (multi-axis alignment) of liquid crystalmolecules is controlled with depressions formed on an insulating layer.The insulating layer is provided to make the thickness of the liquidcrystal layer in a transmission region twice as large as that in areflection region. According to this literature, the depressions are inthe shape of a regular octagon, for example, and projections or slits(electrode openings) are formed at positions opposed to the depressionsvia the liquid crystal layer (see FIGS. 4 and 16 of Literature 7, forexample).

The technology disclosed in Literature 2 or 3 has the followingproblems. Projections or openings are provided in each pixel to form aplurality of liquid crystal domains in the pixel (that is, divide thepixel into domains), to thereby strengthen the alignment regulatingforce on liquid crystal molecules. According to examinations conductedby the inventors of the present invention, however, to obtain sufficientalignment regulating force, it is necessary to form an alignment controlstructure such as projections and openings on both surfaces of theliquid crystal layer (on the surfaces of the pair of substrates opposedeach other facing the liquid crystal layer), and this complicates thefabrication process. Moreover, the effective aperture ratio of a pixelhaving such an alignment regulating structure therein may decrease, andalso the contrast ratio may decrease due to light leakage occurring inthe peripheries of the projections in the pixel. In the case ofproviding the alignment regulating structure on both substrates, thesubstrate alignment margin must be taken into consideration. Therefore,the decrease in effective aperture ratio and/or the decrease in contrastratio will become further conspicuous.

In the technology disclosed in Literature 4, a plurality of liquidcrystal domains are formed in each pixel using wall spacers (thealignment direction of liquid crystal molecules is uniform in one domainand is different among different domains). Therefore, the wall spacersmust be formed inside each pixel, and this causes decrease in effectiveaperture ratio and/or decrease in contrast ratio.

In the technology disclosed in Literature 7, it is necessary to provideprojections or electrode openings at positions opposed to thedepressions formed for control of the multi-axis alignment. Thistechnology therefore has the same problems as those described above.

In any of the literature described above, openings are formed in thedisplay electrodes so that the electroclinic alignment of liquid crystalmolecules is defined with the effect of an electric field generated withapplication of a predetermined voltage. In this relation, when theliquid crystal panel is pressed, the aligned state of liquid crystalmolecules disturbed with the pressing in the pressed portion tends to befixed with the electric field defined with the electrode openings, andthis may result in occurrence of display roughness and degradation indisplay quality.

In view of the above, an object of the present invention is providing avertically aligned liquid crystal display device that can sufficientlystabilize the alignment of liquid crystal molecules with a comparativelysimple construction and can provide display quality equal to or higherthan that conventionally obtained.

Another object of the present invention is providing a liquid crystaldisplay device having a plurality of axisymmetrically aligned domains ineach pixel, in which axisymmetric alignment disturbed when the displayscreen is pressed, for example, can be effectively recovered and thusdisplay failure such as roughness can be reduced to present high displayquality.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, the liquid crystaldisplay device according to the first aspect of the present inventionincludes a first substrate, a second substrate opposed to the firstsubstrate, and a vertically aligned liquid crystal layer interposedbetween the first substrate and the second substrate, wherein the liquidcrystal display device has a plurality of pixels, each pixel including afirst electrode formed on the first substrate, a second electrode formedon the second substrate, and the liquid crystal layer interposed betweenthe first electrode and the second electrode, and a shading regionprovided around the plurality of pixels, a plurality of supports fordefining the thickness of the liquid crystal layer are placed regularlyon a surface of the first substrate or the second substrate facing theliquid crystal layer in the shading region, and the liquid crystal layerhas at least one liquid crystal domain exhibiting axisymmetric alignmentwhen at least a predetermined voltage is applied, and the tilt directionof liquid crystal molecules in the at least one liquid crystal domain isdefined with inclined sides of the plurality of supports.

In one embodiment, each of the at least one liquid crystal domain is incontact with the inclined sides of at least four supports.

In another embodiment, the first electrode has at least one opening, andthe center axis of each of the at least one liquid crystal domain isformed in or near the at least one opening.

In yet another embodiment, the inclined sides of the plurality ofsupports are inclined in an inversely tapered shape with respect to thefirst substrate.

In yet another embodiment, the shape of the plurality of supports alongthe plane parallel to the first substrate plane is roughly a circle, anellipse, a diamond or a cross.

In yet another embodiment, the device further includes a wall structureregularly arranged in the shading region.

In yet another embodiment, the at least one liquid crystal domainincludes two liquid crystal domains, the at least one opening includestwo openings, and the center axes of the axisymmetric alignment of thetwo liquid crystal domains are formed in or near the two openings.

In yet another embodiment, the first electrode includes a transparentelectrode defining a transmission region and a reflective electrodedefining a reflection region.

In yet another embodiment, the at least one liquid crystal domainincludes a liquid crystal domain formed in the transmission region and aliquid crystal domain formed in the reflection region.

In yet another embodiment, the at least one opening includes an openingformed in the transparent electrode and an opening formed in thereflective electrode.

In yet another embodiment, the device further includes: a pair ofpolarizing plates placed to face each other via the first substrate andthe second substrate; and at least one biaxial optical anisotropicmedium layer placed between the first substrate and one of the pair ofpolarizing plates and/or between the second substrate and the otherpolarizing plate.

In yet another embodiment, the device further includes a pair ofpolarizing plates placed to face each other via the first substrate andthe second substrate; and at least one uniaxial optical anisotropicmedium layer placed between the first substrate and one of the pair ofpolarizing plates and/or between the second substrate and the otherpolarizing plate.

The liquid crystal display device according to the second aspect of thepresent invention includes a first substrate having a first electrode, asecond substrate having a second electrode opposed to the firstelectrode, and a vertically aligned liquid crystal layer interposedbetween the first electrode and the second electrode, each of aplurality of pixel regions being defined by the first electrode and thesecond electrode, wherein at least one pixel region among the pluralityof pixel regions is divided into a plurality of sub-pixel regions withdielectric protrusions regularly arranged on the first substrate, andliquid crystal molecules in the liquid crystal layer in each sub-pixelregion are axisymmetrically aligned around an axis vertical to thesurface of the first substrate when a predetermined voltage is appliedbetween the first electrode and the second electrode.

In one embodiment, the pixel region is surrounded with a shading regionas is viewed from top, and the device further includes a wall structureformed to substantially surround the pixel region on the surface of thefirst substrate facing the liquid crystal layer in the shading region.

In another embodiment, the first electrode and/or the second electrodehas an opening formed in the sub-pixel region, and when the voltage isapplied, the vertical axis is formed in or near the opening.

In yet another embodiment, the pixel region is surrounded with a shadingregion as is viewed from top, and a support for defining the thicknessof the liquid crystal layer is formed in the shading region.

In yet another embodiment, the first electrode includes a transparentelectrode and a reflective electrode, and at least one of the pluralityof sub-pixel regions is a transmission region and at least one of thesub-pixel regions is a reflection region.

In yet another embodiment, the relationship 0.3 dt<dr<0.7 dt issatisfied where dt is the thickness of the liquid crystal layer in thetransmission region and dr is the thickness of the liquid crystal layerin the reflection region.

In yet another embodiment, the device further includes a transparentdielectric layer on the surface of the second substrate facing theliquid crystal layer.

In yet another embodiment, the transparent dielectric layer has afunction of scattering light.

In yet another embodiment, the second substrate further includes a colorfilter layer, and the optical density of the color filter layer in thereflection region is lower than the optical density of the color filterlayer in the transmission region.

In yet another embodiment, the device further includes: a pair ofpolarizing plates placed to face each other via the first substrate andthe second substrate; and at least one biaxial optical anisotropicmedium layer placed between the first substrate and one of the pair ofpolarizing plates and/or between the second substrate and the otherpolarizing plate.

In yet another embodiment, the device further includes: a pair ofpolarizing plates placed to face each other via the first substrate andthe second substrate; and at least one uniaxial optical anisotropicmedium layer placed between the first substrate and one of the pair ofpolarizing plates and/or between the second substrate and the otherpolarizing plate.

In yet another embodiment, the pixel region is in the shape of arectangle having a pair of longer sides and a pair of shorter sides, andis divided into the plurality of sub-pixel regions with at least onepair of the dielectric protrusions, and the pair of dielectricprotrusions extend from near the pair of longer sides of the pixelregion in the directions closer to each other and are in line with eachother in the shorter-side direction.

In the liquid crystal display devices according to the first aspect ofthe present invention, in which the supports (wall spacers) for definingthe thickness of the liquid crystal layer are placed regularly in theshading region around the pixels, the inclined sides of the supports actto define the directions in which liquid crystal molecules tilt with anelectric field. Since the supports for defining the thickness of theliquid crystal layer are used as an alignment regulating structure, noadditional step for providing the alignment regulating structure isnecessary. Since the supports are placed in the shading region, decreasein effective aperture ratio and decrease in contrast ratio aresuppressed. By placing the supports so that each of liquid crystaldomains is in contact with the inclined sides of at least four supports,axisymmetrically aligned domains can be formed stably. Further stableformation of axisymmetrically aligned domains is ensured by placing awall structure in the shading region.

In addition, by placing an opening in the first electrode, the centeraxis of the axisymmetric alignment of a liquid crystal domain can befixed in or near the opening. This provides display uniformity, and inparticular, can suppress display roughness observed when the device isviewed at a slanting visual angle.

As described above, according to the first aspect of the presentinvention, a vertically aligned liquid crystal display device that cansufficiently stabilize the alignment of liquid crystal molecules with acomparatively simple construction and can provide display quality equalto or higher than that conventionally obtained is provided.

According to the second aspect of the present invention, the stabilityof the alignment of axisymmetrically aligned (radially tilting) liquidcrystal domains can be enhanced, and thus the display quality of theliquid crystal display device having the conventional wide visual anglecharacteristics can be further improved. Also, in the event of acollapse of the axisymmetric alignment with external force, or adisturbance of the axisymmetric alignment with pressing of the displayscreen, for example, the axisymmetric alignment can be effectivelyrecovered. Hence, a liquid crystal display device with high displayquality that can reduce display failure such as roughness can beprovided. Moreover, since such a liquid crystal display device with highdisplay quality can be implemented with a comparatively simpleconstruction, it can be easily fabricated.

Other features, elements, processes, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B diagrammatically show one pixel of a transmissive LCDdevice 100 of an embodiment according to the first aspect of the presentinvention, in which FIG. 1A is a plan view and FIG. 1B is across-sectional view taken along line 1B-1B′ in FIG. 1A.

FIGS. 2A and 2B diagrammatically show one pixel of another transmissiveLCD device 100′ of an embodiment according to the first aspect of thepresent invention, in which FIG. 2A is a plan view and FIG. 2B is across-sectional view taken along line 2B-2B′ in FIG. 2A.

FIGS. 3A and 3B diagrammatically show one pixel of a transflective LCDdevice 200 of an embodiment according to the first aspect of the presentinvention, in which FIG. 3A is a plan view and FIG. 3B is across-sectional view taken along line 3B-3B′ in FIG. 3A.

FIG. 4 is a plan view of an active matrix substrate 210 a of thetransflective LCD device 200.

FIG. 5 is a cross-sectional view of the active matrix substrate 210 a ofthe transflective LCD device 200.

FIGS. 6A and 6B are diagrammatic views for demonstrating the operationprinciple of the LCD devices of the embodiments according to the firstaspect of the present invention, showing the states during non-voltageapplication (FIG. 6A) and during voltage application (FIG. 6B).

FIG. 7 is a diagrammatic view showing an example of construction of anLCD device according to the first aspect of an embodiment of the presentinvention.

FIG. 8 is a view showing the visual angle—contrast ratio characteristicsof an LCD device of an embodiment according to the first aspect of thepresent invention.

FIGS. 9A and 9B are diagrammatic views for demonstrating the operationprinciple of LCD devices of the present invention, showing the alignedstates of liquid crystal molecules during non-voltage application (FIG.9A) and during voltage application (FIG. 9B).

FIGS. 10A and 10B diagrammatically show one pixel of a transmissive LCDdevice 300, in which FIG. 10A is a plan view as is viewed in thedirection normal to the substrate plane and FIG. 10B is across-sectional view taken along line 10B-10B′ in FIG. 10A.

FIGS. 11A and 11B diagrammatically show one pixel of a transflective LCDdevice 400, in which FIG. 11A is a plan view as is viewed in thedirection normal to the substrate plane and FIG. 11B is across-sectional view taken along line 11B-11B′ in FIG. 11A.

FIGS. 12A to 12C are diagrammatic views of axisymmetrically alignedstates obtained in an embodiment according to the second aspect of thepresent invention and conventionally obtained, in which FIG. 12A showsthe alignment of liquid crystal domains in the steady state beforepressing of the display plane, FIG. 12B shows the alignment after thepressing in a conventional pixel-divided panel, and FIG. 12C shows thealignment after the pressing in a pixel-divided panel of the embodimentof the present invention.

FIG. 13 is a graph showing the voltage-reflectance (transmittance) of atransmission region and a reflection region in a transflective LCDdevice of an embodiment according to the second aspect of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

First, the construction and operation of LCD devices according to thefirst aspect of the present invention will be described.

(Transmissive LCD Device)

A transmissive LCD device 100 of an embodiment according to the firstaspect of the present invention will be described with reference toFIGS. 1A and 1B. FIGS. 1A and 1B diagrammatically show one pixel of thetransmissive LCD device 100, in which FIG. 1A is a plan view and FIG. 1Bis a cross-sectional view taken along line 1B-1B′ in FIG. 1A. FIG. 1Bdiagrammatically shows the aligned state of liquid crystal molecules 121exhibited when a predetermined voltage (voltage equal to or higher thana threshold voltage) is applied to the liquid crystal layer.

The LCD device 100 includes a transparent substrate (for example, aglass substrate) 110 a, a transparent substrate 110 b placed to face thetransparent substrate 110 a, and a vertically aligned liquid crystallayer 120 interposed between the transparent substrates 110 a and 110 b.Vertical alignment films (not shown) are formed on the surfaces of thesubstrates 110 a and 110 b facing the liquid crystal layer 120. Duringnon-voltage application, therefore, the liquid crystal molecules in theliquid crystal layer 120 are aligned roughly vertical to the surfaces ofthe vertical alignment films. The liquid crystal layer 120 includes anematic liquid crystal material having negative dielectric anisotropyand also includes a chiral agent as required.

The LCD device 100 further includes pixel electrodes 111 formed on thetransparent substrate 110 a and a counter electrode 131 formed on thetransparent substrate 110 b. Each pixel electrode 111, the counterelectrode 131 and the liquid crystal layer 120 interposed between theseelectrodes define a pixel. In the illustrated example, both the pixelelectrodes 111 and the counter electrode 131 are formed of a transparentconductive film (for example, an ITO film). Typically, color filters 130(the entire of the plurality of color filters may also be called a colorfilter layer 130) provided for the respective pixels, as well as a blackmatrix (shading layer) 132 formed in the gaps between the adjacent colorfilters 130, are formed on the surface of the transparent substrate 110b facing the liquid crystal layer 120, and the counter electrode 131 isformed on the color filters 130 and the black matrix 132. Alternatively,the color filters 130 and the black matrix 132 may be formed on thecounter electrode 131 (on the surface thereof facing the liquid crystallayer 120).

The LCD device 100 has a shading region between the adjacent pixels, andsupports (wall spacers) 133 are formed on the transparent substrate 110a in the shading region. The supports 133 define the thickness (alsocalled a cell gap) dt of the liquid crystal layer 120. The shadingregion as used herein refers to a region shaded from light with thepresence of TFTs (not shown), gate signal lines 102 and source signallines 103 formed on the peripheries of the pixel electrodes 111 on thetransparent substrate 110 a, or the presence of the black matrix formedon the transparent substrate 110 b, for example. Since this region doesnot contribute to display, the supports 133 formed in the shading regionis free from adversely affecting the display.

In the LCD device 100, the supports 133 are placed at the crossings ofthe gate signal lines 102 and the source signal lines 103, to correspondto the four corners of each pixel roughly in the shape of a square. Eachsupport 133 has a cross shape in the plane parallel to the transparentsubstrate 110 a, composed of a portion parallel to the gate signal line102 and a portion parallel to the source signal line 103. The support133 has inclined sides, to act to define the directions in which theliquid crystal molecules 121 tilt with the inclined sides. This worksbecause the liquid crystal molecules 121 attempt to align roughlyvertical to the inclined sides (strictly, to the vertical alignment filmon the inclined sides) and thus are alignment-regulated toward thedirections corresponding to the tilt directions and angles of theinclined sides. This alignment regulating force acts even duringnon-voltage application. The illustrated inclined sides of the supports133 are inclined in an inversely tapered shape with respect to thetransparent substrate 110 a. This inclination is preferred because thealignment regulation directions given with the inclined sides agree withalignment regulation directions given with an inclined electric fieldgenerated near an opening 114 in the pixel electrode 111 formed on thetransparent substrate 116 a.

The shape of the supports 133 in the plane parallel to the transparentsubstrate 110 a is not limited to a cross, but the supports 133 may beroughly in the shape of a polygon such as a circle, an ellipse and adiamond. The inclined sides of the supports 133 define the directions oftilt of the liquid crystal molecules 121 and act to define the outeredges of axisymmetrically aligned domains. Therefore, the shape of thesupports 133 may be determined so that the axisymmetric alignment of theliquid crystal domains can be stably formed, depending on the shape ofthe liquid crystal domains and the positions of placement of thesupports 133. The supports 133 can be formed in a photolithographicprocess using a photosensitive resin, for example. The supports 133 maybe formed on any of the transparent substrates 110 a and 110 b. Asdescribed above, however, to obtain the supports 133 having inclinedsides inversely tapered with respect to the transparent substrate 110 a,it is easy to form tapered supports on the transparent substrate 110 b,and thus it is preferred to form the supports 133 on the transparentsubstrate 110 b.

The pixel electrode 111 has the opening 114 formed at a predeterminedposition. When a predetermined voltage is applied across the liquidcrystal layer 120, a liquid crystal domain having axisymmetric alignmentis formed, with the center axis of the axisymmetric alignment thereofbeing in or near the opening 114. As will be described later, theopening 114 formed in the pixel electrode 111 acts to fix the positionof the center axis of the axisymmetric alignment. An inclined electricfield is generated near the opening 114 with the voltage applied betweenthe pixel electrode 111 and the counter electrode 113. With the inclinedelectric field, the directions of tilt of the liquid crystal moleculesare defined, to thereby cause the action described above.

The shape of the opening 114 provided to fix/stabilize the center axisof the axisymmetrically aligned domains is preferably circular asillustrated, but not limited to this. To exert roughly equal alignmentregulating force in all directions, the shape is preferably a polygonhaving four or more sides and more preferably a regular polygon.

In the LCD device 100, when a predetermined voltage (voltage equal to orhigher than a threshold voltage) is applied between the pixel electrode111 and the counter electrode 131, an axisymmetrically aligned domain ofwhich the center axis is fixed/stabilized in or near the opening 114 isformed. The alignment regulating force of the inclined sides of thesupports 133 provided on the periphery of the pixel define thedirections in which the liquid crystal molecules 121 existing near theouter edges of the liquid crystal domain fall. The inclined electricfield generated near the opening 114 in the pixel electrode 111 definesthe directions in which the liquid crystal molecules 121 near theopening 114 fall. The alignment regulating force of the inclined sidesof the supports 133 and the alignment regulating force of the opening114 are considered to act cooperatively, to stabilize the axisymmetricalignment of the liquid crystal domain.

The transparent substrate 110 a, together with the circuit elements suchas the TFTs (not shown), the gate signal lines 102 and the source signallines 103 connected to the TFTs, a gate insulating film 104, aprotection layer 105, the pixel electrodes 111, the supports 133, thealignment film (not shown) and the like formed on the surface of thetransparent substrate 110 a facing the liquid crystal layer 120, arecollectively called an active matrix substrate in some cases. Likewise,the transparent substrate 110 b, together with the color filter layer130, the black matrix 132, the counter electrode 131, the alignment filmand the like formed on the transparent substrate 110 b, are collectivelycalled a counter substrate or a color filter substrate in some cases.

Although omitted in the above description, the LCD device 100 furtherincludes a pair of polarizing plates placed to face each other via thetransparent substrates 110 a and 110 b. The polarizing plates aretypically placed so that their transmission axes are orthogonal to eachother. The LCD device 100 may further include a biaxial opticalanisotropic medium layer and/or a uniaxial optical anisotropic mediumlayer, as will be described later.

FIGS. 2A and 2B diagrammatically show another transmissive LCD device100′ of an embodiment according to the first aspect of the presentinvention. Components having substantially the same functions as thoseof the LCD 100 shown in FIGS. 1A and 1B are denoted by the samereference numerals, and the description thereof is omitted here. FIG. 2Ais a plan view and FIG. 2B is a cross-sectional view taken along line2B-2B′ in FIG. 2A.

The LCD device 100′ has a wall structure 115 on the transparentsubstrate 100 a, and supports 133 are formed on the wall structure 115.The wall structure 115 acts to form axisymmetrically aligned domainswith the alignment regulating force of the wall sides thereof, as in thecase of the supports 133. The wall structure 115 may be formed on anyone of the transparent substrates 110 a and 110 b. If inversely taperedwall sides are to be given, like the inclined sides of the supports 133,the wall structure 115 is preferably formed on the transparent substrate110 b. In this case, however, the number of fabrication steps willdisadvantageously increase. If the wall structure 115 is formed on thetransparent substrate 110 a (active matrix substrate), the wallstructure 115 can be formed integrally with an interlayer insulatingfilm by adjusting the exposure in the process for forming the interlayerinsulating film using a photosensitive resin, for example. In this case,the wall faces of the wall structure 115 tend to be tapered. It ishowever possible to reduce the disagreement between the alignmentregulating force of the wall faces and the alignment regulating force ofthe inversely tapered inclined sides of the supports 133 by setting thetilt angle at 40° or more. Naturally, it is more preferred to form thewall structure having inversely tapered wall faces (tilt angle exceeding90°).

The wall structure 115 has a portion formed in the shading region aroundeach pixel to substantially surround the pixel and a pair of extendedportions extending toward the center of the pixel from the portionsurrounding the pixel at the positions bisecting the pixel in the lengthdirection. The extended portions of the wall structure 115 act to definetwo liquid crystal domains formed in the pixel. The extended portionsare preferably formed in a region in which a line (for example, astorage capacitance line (not shown)) extends because in such a regionthe extended portions are free from adversely affecting the display. Thewall structure 115 shown in the illustrated example is a continuouswall, but may be composed of a plurality of separate walls. The wallstructure 115, which acts to define boundaries of liquid crystal domainslocated near the outer edges of the pixel, should preferably have alength of some extent. For example, when the wall structure is composedof a plurality of walls, each wall is preferably longer than the gapbetween the adjacent walls.

The supports 133 are provided to correspond to the four corners of eachof the two liquid crystal domains formed in each pixel, and act todefine the boundaries of the liquid crystal domains. The positions ofthe supports 133 are not limited to on the wall structure 115 formed inthe shading region as illustrated. In the case of forming the supports133 on the wall structure 115, setting is made so that the sum of theheight of the wall structure 115 and the height of the supports 133 isequal to the thickness dt of the liquid crystal layer 120. If thesupports 133 are formed in a region having no wall structure 115,setting is made so that the height of the supports 133 is equal to thethickness dt of the liquid crystal layer 120. To sufficiently exert thealignment regulating force of the side faces of the supports 133, theheight of the supports 133 is preferably larger than the height of thewall structure 115. The supports 133 may be formed on any one of thetransparent substrates 110 a and 110 b, but preferably is formed on thetransparent substrate 110 b as described above. In the illustrateexample, the supports 133 are roughly in the shape of a circle, but theshape can be appropriately changed as in the case described above.

The pixel electrode 111 has two openings 114 in roughly the centers oftwo liquid crystal domains of which the boundaries are defined with thesupports 133 and the wall structure 115. When a predetermined voltage isapplied across the liquid crystal layer 120, liquid crystal domainshaving axisymmetric alignment are formed, with the center axes of theaxisymmetric alignment thereof being in or near the openings 114. Inthis way, the alignment regulating force of the inclined sides of thesupports 133 and the wall faces of the wall structure 115 and thealignment regulating force of the openings 114 are considered to actcooperatively, to stabilize the axisymmetric alignment of the liquidcrystal domains. The shape of the openings 114 may be changedappropriately as described above.

(Transflective LCD Device)

Next, a transflective LCD device 200 of an embodiment according to thefirst aspect of the present invention will be described with referenceto FIGS. 3A and 3B.

FIGS. 3A and 3B diagrammatically show one pixel of the transflective LCDdevice 200 of the embodiment of the present invention, in which FIG. 3Ais a plan view and FIG. 3B is a cross-sectional view taken along line3B-3B′ in FIG. 3A.

The LCD device 200 includes a transparent substrate (for example, aglass substrate) 210 a, a transparent substrate 210 b placed to face thetransparent substrate 210 a, and a vertically aligned liquid crystallayer 220 interposed between the transparent substrates 210 a and 210 b.Vertical alignment films (not shown) are formed on the surfaces of thesubstrates 210 a and 210 b facing the liquid crystal layer 220. Duringnon-voltage application, therefore, liquid crystal molecules in theliquid crystal layer 220 are aligned roughly vertical to the surfaces ofthe vertical alignment films. The liquid crystal layer 220 includes anematic liquid crystal material having negative dielectric anisotropyand also includes a chiral agent as required.

The LCD device 200 further includes pixel electrodes 211 formed on thetransparent substrate 210 a and a counter electrode 231 formed on thetransparent substrate 210 b. Each pixel electrode 211, the counterelectrode 231 and the liquid crystal layer 220 interposed between theseelectrodes define a pixel. Circuit elements such as TFTs are formed onthe transparent substrate 210 a as will be described later. Herein, thetransparent substrate 210 a and the components formed thereon arecollectively called an active matrix substrate 210 a in some cases.

Typically, color filters 230 (the entire of the plurality of colorfilters may also be called a color filter layer 230) provided for therespective pixels, as well as a black matrix (shading layer) 232provided in the gaps between the adjacent color filters 230, are formedon the surface of the transparent substrate 210 b facing the liquidcrystal layer 220, and the counter electrode 231 is formed on the colorfilters 230 and the black matrix 232. Alternatively, the color filters230 and the black matrix 232 may be formed on the counter electrode 231(on the surface thereof facing the liquid crystal layer 220). Herein,the transparent substrate 210 b and the components formed thereon arecollectively called a counter substrate (color filter substrate) 210 bin some cases.

Each pixel electrode 211 includes a transparent electrode 211 a formedof a transparent conductive layer (for example, an ITO layer) and areflective electrode 211 b formed of a metal layer (for example, an Allayer, an alloy layer including Al, and a layered film including any ofthese layers). Having such a pixel electrode, each pixel includes atransmission region A defined by the transparent electrode 211 a and areflection region B defined by the reflective electrode 211 b, toprovide display in the transmission mode and display in the reflectionmode, respectively.

The LCD device 200 has a wall structure 215 formed on the transparentsubstrate 210 a, and supports 233 are formed on the wall structure 215.The wall structure 215 acts to form axisymmetrically aligned domainswith the alignment regulating force of the wall faces thereof, as dosupports 233. The wall structure 215 has a portion formed in the shadingregion around each pixel to substantially surround the pixel and twopairs of extended portions extending toward the center of the pixel fromthe portion surrounding the pixel to divide the pixel into three in thelength direction.

One of the pairs of extended portions are formed at positions near theboundary between the transmission region A and the reflection region B,and the other pair of extended portions are formed at positionsbisecting the transmission region in the length direction. The supports233 are provided to correspond to the four corners of each of the threeliquid crystal domains formed in the pixel, and act to define theboundaries the liquid crystal domains. The alignment regulating force ofthe inclined sides of the supports 233 placed as described above and thealignment regulating force of the wall faces of the wall structure 115define the directions in which liquid crystal molecules fall duringvoltage application, to form three liquid crystal domains (two in thetransmission region A and one in the reflection region B).

The pixel electrode 211 has three openings 214 formed to correspond toabout the centers of three liquid crystal domains. When a predeterminedvoltage is applied across the liquid crystal layer 220, three liquidcrystal domains having axisymmetric alignment are formed, with thecenter axes of the axisymmetric alignment thereof being in or near theopenings 214. The openings 214 formed in the pixel electrode 211 act tofix the positions of the center axes of the axisymmetric alignment. Aninclined electric field is generated near the openings 214 with thevoltage applied between the pixel electrode 211 and the counterelectrode 213. With the inclined electric field, the directions of tiltof the liquid crystal molecules are defined, to thereby cause the actiondescribed above.

The placement of the supports 233, the wall structure 215 and theopenings 214 and preferred shapes thereof are similar to the case of thetransmissive LCD device 100′ described above. In FIGS. 3A and 3B, thetransmission region A has two liquid crystal domains and the reflectionregion B has one liquid crystal domain. However, the arrangement is notlimited to this. Each liquid crystal domain is preferably roughly squarein shape from the standpoint of the viewing angle characteristics andthe stability of alignment. The wall structure 215 may be omitted.

In the LCD device 200, when a predetermined voltage (voltage equal to orhigher than a threshold voltage) is applied between the pixel electrode211 and the counter electrode 231, three axisymmetrically aligneddomains are formed with the center axes thereof being stabilized in ornear the three openings 214. The eight supports 233 and the wallstructure 215 define the directions in which liquid crystal molecules inthe three adjacent liquid crystal domains fall with an electric field,and also stabilize the boundaries of the liquid crystal domains locatednear the outer edges of the pixel.

Next, a preferred construction specific to the transflective LCD device200 permitting both the transmission-mode display and thereflection-mode display will be described.

While light used for display passes through the liquid crystal layer 220once in the transmission-mode display, it passes through the liquidcrystal layer 220 twice in the reflection-mode display. Accordingly, asdiagrammatically shown in FIG. 3B, the thickness dt of the liquidcrystal layer 220 in the transmission region A is preferably set roughlydouble the thickness dr of the liquid crystal layer 220 in thereflection region B. By setting in this way, the retardation given tothe light by the liquid crystal layer 220 can be roughly the same inboth display modes. Most preferably, dr=0.5 dt should be satisfied, butgood display is secured in both display modes as long as 0.3 dt<dr<0.7dt is satisfied. Naturally, dt=dr may be satisfied depending on the use.

In the LCD device 200, a transparent dielectric layer 234 is provided onthe glass substrate 210 b only in the reflection region B to make thethickness of the liquid crystal layer 220 in the reflection region Bsmaller than that in the transmission region A. This constructioneliminates the necessity of providing a step by forming an insulatingfilm and the like under the reflective electrode 211 b, and thus has theadvantage of simplifying the fabrication of the active matrix substrate210 a. If the reflective electrode 211 b is formed on such an insultingfilm provided to give a step for adjusting the thickness of the liquidcrystal layer 220, light used for transmission display will be shadedwith the reflective electrode covering a slope (tapered face) of theinsulating film, or light reflected from the reflective electrode formedon a slope of the insulating film will repeat internal reflection,failing to be effectively used even for reflection display. By adoptingthe construction described above, occurrence of such problems isprevented, and thus the light use efficiency can be improved.

If the transparent dielectric layer 234 is provided with a function ofscattering light (diffuse reflection function), good white display closeto paper white can be realized without the necessity of providing thereflective electrode 211 b with the diffuse reflection function. Suchwhite display close to paper white can also be realized by making thesurface of the reflective electrode 211 b uneven, and in this case, nolight scattering function is necessary for the transparent dielectriclayer 234. However, the uneven surface may fail to stabilize theposition of the center axis of the axisymmetric alignment depending onthe shape of the uneven surface. On the contrary, by combining thetransparent dielectric layer 234 having the light scattering functionand the reflective electrode 211 b having a flat surface, the positionof the center axis can be stabilized with the opening 214 (the shadingconductive layer 216 b) formed in the reflective electrode 211 b morereliably. Note that in the case of making the surface of the reflectiveelectrode 211 b uneven to provide the reflective electrode 211 b withthe diffuse reflection function, the uneven shape is preferably acontinuous wave shape to prevent occurrence of an interference color,and such a shape is preferably set to allow stabilization of the centeraxis of the axisymmetric alignment.

While light used for display passes through the color filter layer 230once in the transmission mode, it passes through the color filter layer230 twice in the reflection mode. Accordingly, if the color filter layer230 has the same optical density both in the transmission region A andthe reflection region B, the color purity and/or the luminance maydecrease in the reflection mode. To suppress occurrence of this problem,the optical density of the color filter layer in the reflection regionis preferably made lower than that in the transmission region. Theoptical density as used herein is a characteristic value characterizingthe color filter layer. For example, the optical density can be reducedby reducing the thickness of the color filter layer. Otherwise, theoptical density can be reduced by reducing the density of a pigmentadded, for example, while keeping the thickness of the color filterlayer unchanged.

Next, referring to FIGS. 4 and 5, an example of the structure of anactive matrix substrate suitably used for the transflective LCD devicewill be described. FIG. 4 is a partial enlarged view of the activematrix substrate, and FIG. 5 is a cross-sectional view taken along lineX-X′ in FIG. 4. The active matrix substrate shown in FIGS. 4 and 5 canbe the same in construction as the active matrix substrate 211 a shownin FIGS. 3A and 3B, except that one liquid crystal domain is formed inthe transmission region A (that is, the number of the openings 214 isreduced).

The active matrix substrate shown in FIGS. 4 and 5 has a transparentsubstrate 1 made of a glass substrate, for example. Gate signal lines 2and source signal lines 3 run on the transparent substrate 1 to crosseach other at right angles. TFTs 4 are formed near the crossings ofthese signal lines 2 and 3. Drain electrodes 5 of the TFTs 4 areconnected to corresponding pixel electrodes 6.

Each of the pixel electrode 6 includes a transparent electrode 7 made ofa transparent conductive layer such as an ITO layer and a reflectiveelectrode 8 made of Al and the like. The transparent electrode 7 definesa transmission region A, and the reflective electrode 8 defines areflection region B. Openings 15 are formed at predetermined positionsof the pixel electrode 6 for fixing/stabilizing the center axes of theaxisymmetrically aligned domains as described above.

The pixel electrode 6 overlaps the gate signal line for the next row viaa gate insulating film 9, forming a storage capacitance. The TFT 4 has amultilayer structure including the gate insulating film 9, asemiconductor layer 12, a channel protection layer 13 and an n⁺-Si layer11 (source/drain electrodes) formed in this order on a gate electrode 10branched from the gate signal line 2.

Supports 33 may be formed in the region surrounding each pixel electrode6 on the active matrix substrate, or may be formed on the countersubstrate so that the supports 33 exist in the region surrounding eachpixel electrode 6 when the counter substrate is bonded with the activematrix substrate. The wall structure 215 may be formed in the regionsurrounding each pixel electrode 6 on the active matrix substrate.

The illustrated TFT is of a bottom gate type. The TFT is not limited tothis type, but a top gate type TFT can also be used.

As described above, in the LCD device 200 having the constructiondescribed in FIGS. 3A and 3B, the alignment of liquid crystal moleculesis regulated using the supports 233 for defining the thickness of theliquid crystal layer 220. The wall structure 215 for stable formation ofliquid crystal domains and the openings 214 for fixing/stabilizing thecenter axes may only be formed on one of the substrates. With thiscomparatively simple construction, the alignment of liquid crystalmolecules can be sufficiently stabilized. In addition, with theplacement of the transparent dielectric layer 234 and/or the colorfilter 230 in the manner described above, the display brightness andcolor purity in both the transmission mode and the reflection mode canbe improved.

(Operation Principle)

The reason why the LCD device having a vertically aligned liquid crystallayer in the first aspect of the present invention has excellent wideviewing angle characteristics will be described with reference to FIGS.6A and 6B.

FIGS. 6A and 6B are views for demonstrating how the alignment regulatingforce of an opening 15 formed in the pixel electrode 6 acts, in whichthe aligned states of liquid crystal molecules during non-voltageapplication (FIG. 6A) and during voltage application (FIG. 6B) arediagrammatically shown.

The LCD device shown in FIGS. 6A and 6B includes an insulating film 16,a pixel electrode 6 having an opening 15 and an alignment film 12 formedin this order on a transparent substrate 1. The LCD device also includesa color filter layer 18, a counter electrode 19, supports 33, and analignment film 32 formed in this order on another transparent substrate17. Although omitted in FIGS. 6A and 6B, the alignment film 32 is formedto cover the supports 33. A liquid crystal layer 20 interposed betweenthe two substrates includes liquid crystal molecules 21 having negativedielectric anisotropy.

As shown in FIG. 6A, during non-voltage application, the liquid crystalmolecules 21 are aligned roughly vertical to the substrate surface withthe alignment regulating force of the vertical alignment films 12 and32. The supports 33 have inclined sides inversely tapered with respectto the substrate 1. The liquid crystal molecules 21 near the inclinedsides of the supports 33 attempt to align roughly vertical to theinclined sides, and thus tilt with respect to the surface of thesubstrate 1.

As shown in FIG. 6B, during voltage application, the liquid crystalmolecules 21 having negative dielectric anisotropy attempt to make theirmajor axes vertical to electric lines of force, and this causes thedirections in which the liquid crystal molecules 21 fall to be definedwith an inclined electric field generated around the opening 15. Also,the liquid crystal molecules 21 near the supports 33 attempt to furthertilt in the direction in which the liquid crystal molecules 21 havealready tilted with the alignment regulating force of the inclined sidesof the supports 33. Hence, the liquid crystal molecules are alignedaxisymmetrically around the opening 15 as the center, for example. Inthe resultant axisymmetrically aligned domain, the liquid crystaldirectors point to all directions (directions in the substrate plane),and thus, excellent viewing angle characteristics can be obtained.

When a wall structure is additionally provided, the wall structuredefines the directions in which the liquid crystal molecules 21 fallwith the alignment regulating force of the side faces (wall faces)thereof. Typically, since the wall structure is covered with a verticalalignment film, the alignment regulating force exerts to align theliquid crystal molecules vertical to the wall faces. The wall faces ofthe wall structure are preferably inclined in the same direction as thesupports 33.

Next, an example of more specific construction of the LCD deviceaccording to the first aspect of the present invention will be describedwith reference to FIG. 7.

The LCD device shown in FIG. 7 includes: a backlight; a transflectiveliquid crystal panel 50; a pair of polarizing plates 40 and 43 placed toface each other via the transflective liquid crystal panel 50; quarterwave plates 41 and 44 respectively placed between the polarizing plates40 and 43 and the liquid crystal panel 50; and phase plates 42 and 45having negative optical anisotropy respectively placed between the waveplates 41 and 44 and the liquid crystal panel 50. The liquid crystalpanel 50 includes a vertically aligned liquid crystal layer 20 between atransparent substrate (active matrix substrate) 1 and a transparentsubstrate (counter substrate) 17. As the liquid crystal panel 50, onehaving the same construction as that of the LCD device 200 shown inFIGS. 3A and 3B is used.

The display operation of the LCD device shown in FIG. 7 will be brieflydescribed.

In reflection-mode display, light incident from above passes through thepolarizing plate 43 to be output as linearly polarized light. Thelinearly polarized light is changed to circularly polarized light withthe quarter wave plate 44 placed so that the slower axis thereof forms45′ with the transmission axis of the polarizing plate 43. Thecircularly polarized light passes through the color filter layer (notshown) formed on the substrate 17. In the illustrated example, the phaseplate 45 provides no phase difference for light incident in the normaldirection.

During non-voltage application, in which liquid crystal molecules in theliquid crystal layer 20 are aligned roughly vertical to the substrateplane, incident light passes through the liquid crystal layer 20 with aphase difference of roughly 0 and is reflected with the reflectiveelectrode formed on the lower substrate 1. The reflected circularlypolarized light passes again through the liquid crystal layer 20 and thecolor filter layer. The light then passes through the phase plate 45having negative optical anisotropy as the circularly polarized light, toenter the quarter wave plate 44, where the light is changed to linearlypolarized light having a polarizing direction orthogonal to thepolarizing direction given to the incident light after first passingthrough the polarizing plate 43, and reaches the polarizing plate 43.The resultant linearly polarized light fails to pass through thepolarizing plate 43, and thus black display is provided.

During voltage application, in which the liquid crystal molecules in theliquid crystal layer 20 are tilted toward the horizontal direction fromthe direction vertical to the substrate plane, the incident circularlypolarized light is changed to elliptically polarized light due tobirefringence of the liquid crystal layer 20, and reflected with thereflective electrode formed on the lower substrate 1. The polarizedstate of the reflected light is further changed during passing backthrough the liquid crystal layer 20. The reflected light passes againthrough the color filter layer and then the phase plate 45 havingnegative optical anisotropy, to enter the quarter wave plate 44 as theelliptically polarized light. Accordingly, when reaching the polarizingplate 43, the light is not linearly polarized light having a polarizingdirection orthogonal to the polarizing direction given to the originalincident light, and thus passes through the polarizing plate 43. That isto say, by adjusting the applied voltage, the degree of the tilt of theliquid crystal molecules can be controlled, and thus the amount ofreflected light allowed to pass through the polarizing plate 43 can bechanged, to thereby enable grayscale display.

In transmission-mode display, the upper and lower polarizing plates 43and 40 are placed so that the transmission axes thereof are orthogonalto each other. Light emitted from a light source is changed to linearlypolarized light at the polarizing plate 40, and then changed tocircularly polarized light when being incident on the quarter wave plate41 placed so that the slower axis thereof forms 450 with thetransmission axis of the polarizing plate 40. The circularly polarizedlight then passes through the phase plate 42 having negative opticalanisotropy and is incident on the transmission region A of the lowersubstrate 1. In the illustrated example, the phase plate 42 provides nophase difference for light incident in the normal direction.

During non-voltage application, in which liquid crystal molecules in theliquid crystal layer 20 are aligned roughly vertical to the substrateplane, the incident light passes through the liquid crystal layer 20with a phase difference of roughly 0. That is, the light incident on thelower substrate 1 as circularly polarized light passes through theliquid crystal layer 20 and then the upper substrate 17 in this state.The light then passes through the upper phase plate 45 having negativeoptical anisotropy, to enter the quarter wave plate 44. The lower andupper quarter wave plates 41 and 44 are placed so that the slower axesthereof are orthogonal to each other. Therefore, a phase difference inthe polarized light that has entered the quarter wave plate 44, whichwas given at the lower quarter wave plate 41, can be cancelled with thequarter wave plate 44, and thus the light resumes the original linearlypolarized light. The polarized light coming from the upper quarter waveplate 44 is therefore linearly polarized light having the polarizingdirection parallel with the transmission axis (polarizing axis) of thepolarizing plate 40, and thus absorbed with the polarizing plate 43 ofwhich the transmission axis is orthogonal to that of the polarizingplate 40. Accordingly, black display is provided.

During voltage application, in which the liquid crystal molecules in theliquid crystal layer 20 are tilted toward the horizontal direction fromthe direction vertical to the substrate plane, the incident circularlypolarized light is changed to elliptically polarized light due tobirefringence of the liquid crystal layer 20. The light then passesthrough the color filter layer 17, the phase plate 45 having negativeoptical anisotropy, and the quarter wave plate 44 as the ellipticallypolarized light. Accordingly, when reaching the polarizing plate 43, thelight is not linearly polarized light orthogonal to the polarizedcomponent in the original incident light, and thus passes through thepolarizing plate 43. That is to say, by adjusting the applied voltage,the degree of the tilt of the liquid crystal molecules can becontrolled, and thus the amount of light allowed to pass through thepolarizing plate 43 can be changed, to thereby enable grayscale display.

The phase plate having negative optical anisotropy minimizes the amountof change in phase difference occurring with change of the viewing anglewhen the liquid crystal molecules are in the vertically aligned state,and thus suppresses black floating observed when the display device isviewed at a wide viewing angle. In place of the combination of the phaseplate having negative optical anisotropy and the quarter wave plate, abiaxial phase plate unifying the functions of both plates may be used.

When axisymmetrically aligned domains are used to implement the normallyblack mode that presents black display during non-voltage applicationand white display during voltage application, as in the presentinvention, a polarizing plate-caused extinction pattern can beeliminated by placing a pair of quarter wave plates on the top andbottom of the LCD device (panel), and thus the brightness can beimproved. Also, when axisymmetrically aligned domains are used toimplement the normally black mode with upper and lower polarizing platesplaced so that the transmission axes thereof are orthogonal to eachother, it is theoretically possible to present black display ofsubstantially the same level as that obtained when a pair of polarizingplates are placed under crossed nicols. Therefore, a considerably highcontrast ratio can be obtained, and also, with the all-directionalignment of liquid crystal molecules, wide viewing anglecharacteristics can be attained.

The thicknesses dt and dr of the liquid crystal layer in thetransmission region and the reflection region defined in the presentinvention preferably has the relationship satisfying 0.3 dt<dr<0.7 dt,more preferably 0.4 dt<dr<0.6 dt, as is found from the dependence of thevoltage-reflectance (transmittance) of the transmission region and thereflection region on the thickness of the liquid crystal layer shown inFIG. 8. If the thickness of the liquid crystal layer in the reflectionregion is smaller than the lower limit, the reflectance will be 50% orless of the maximum reflectance, failing to provide sufficiently highreflectance. If the thickness dr of the liquid crystal layer in thereflection region is greater than the upper limit, the peak of thereflectance in the voltage-reflectance characteristics exists at a drivevoltage different from that in the case of the transmission display.Also, the relative reflectance tends to be low at a white displayvoltage optimal for the transmission display. The reflectance is as lowas 50% or less of the maximum reflectance, failing to providesufficiently high reflectance. Since the optical length in the liquidcrystal layer in the reflection region B is double that in thetransmission region, the birefringence anisotropy (Δn) of the liquidcrystal material and the panel cell thickness design are very importantwhen the same design is made for both the transmission region and thereflection region.

Example 1

Specific characteristics of the transflective LCD device of theembodiment according to the first aspect of the present invention willbe described.

An LCD device having the construction shown in FIG. 7 was fabricated. Asthe liquid crystal cell 50, one having the same construction as the LCDdevice 200 shown in FIGS. 3A and 3B was used. A transparent dielectriclayer having no light scattering function was formed as the transparentdielectric layer 234, and a resin layer having a continuous unevensurface was formed under the reflective electrode 211 b, to adjust thediffuse reflection characteristics in the reflection display. The unevensurface was formed by the method described in Japanese Laid-Open PatentPublication No. 9-90426.

The openings 214 and the wall structure 215 in the LCD device 200 shownin FIGS. 3A and 3B were omitted, so that the alignment regulation wasmade with the supports 233. Cross-shaped supports (the shape of thesupports 133 in FIG. 1A) were used as the supports 233. The supports 233were formed on the counter substrate by photolithography using anegative photosensitive resin (for example, V-259PA (Nippon SteelChemical Co., Ltd.)). The inclined sides were inversely tapered withrespect to the counter substrate, and the tilt angle (angle formedbetween the substrate surface and the inclined side) was about 45°.

The vertical alignment films were formed using a known alignment filmmaterial by a known method. No rubbing was made. A liquid crystalmaterial having negative dielectric anisotropy (Δn: 0.1 and Δ∈: −4.5)was used. In this example, the thicknesses dt and dr of the liquidcrystal layer in the transmission region and the reflection region wereset at 4 μm and 2.2 μm, respectively (dr=0.55 dt).

The resultant liquid crystal cell was sandwiched between two orthogonalpolarizing plates, and observed. As a result, it was confirmed thatliquid crystal molecules near the supports continuously fell along theinclined sides of the supports during voltage application, formingaxisymmetric liquid crystal domains.

The LCD device of this example had a multilayer structure composed of apolarizing plate (observer side), a quarter wave plate (phase plate 1),a phase plate having negative optical anisotropy (phase plate 2 (NRplate)), the liquid crystal layer (on the upper and lower sides thereof,the color filter substrate and the active matrix substrate wererespectively placed), a phase plate having negative optical anisotropy(phase plate 3 (NR plate)), a quarter wave plate (phase plate 4), and apolarizing plate (backlight side) in the order from the observer side.The upper and lower quarter wave plates (phase plates 1 and 4) wereplaced so that the slower axes thereof were orthogonal to each other,and had a phase difference of 140 nm. The phase plates having negativeoptical anisotropy (phase plates 2 and 3) had a phase difference of 135nm. The two polarizing plates were placed so that the absorption axesthereof were orthogonal to each other.

A drive signal was applied to the thus-obtained LCD device (4V wasapplied across the liquid crystal layer) to evaluate the displaycharacteristics.

The results of the visual angle—contrast characteristics in thetransmission display are shown in FIG. 8. The viewing anglecharacteristics in the transmission display were roughly symmetric inall directions, the range CR>10 was as large as up to ±80°, and thetransmission contrast was as high as 300:1 or more at the front.

As for the characteristics of the reflection display, the reflectanceevaluated with a spectral calorimeter (CM2002 from Minolta Co., Ltd.)was about 8.4% (value in terms of the aperture ratio of 100%) withrespect to a standard diffuse plate as the reference. The contrast valueof the reflection display was 21, which was high compared with the caseof the conventional LCD devices.

Example 2

As in Example 1, an LCD device having the construction shown in FIG. 7was fabricated using a liquid crystal cell having the same constructionas the LCD device 200 shown in FIGS. 3A and 3B. A transparent dielectriclayer having no light scattering function was formed as the transparentdielectric layer 234, and a resin layer having a continuous unevensurface was formed under the reflective electrode 211 b, to adjust thediffuse reflection characteristics in the reflection display. The wallstructure 215 was formed integrally with the resin layer (interlayerinsulating film) formed under the reflective electrode 211 b forimparting an uneven shape on the surface of the reflective electrode 211b.

Specifically, the active matrix substrate of this example was formed inthe following manner.

First, a positive photosensitive resin layer was formed to cover thecircuit elements such as TFTs under predetermined conditions. Thephotosensitive resin layer was exposed to light using a first photomaskthat shades portions corresponding to regions that are to be projectionsof an uneven shape and regions that are to be the wall structure underlow-light conditions (80 mJ/cm²), to thereby form the uneven shape onthe surface of the regions of the photosensitive resin layer underlyingthe reflective electrodes and also form the wall structure (see the wallstructure 215 in FIGS. 3A and 3B). Subsequently, for formation ofcontact holes, the photosensitive resin layer was exposed to light usinga second photomask that is open for regions corresponding to the contactholes under high-light conditions (350 mJ/cm²). Thereafter, a series ofprocessing such as development, drying and baking followed. In this way,the interlayer insulating film and the wall structure were formed fromthe same photosensitive resin layer in a one-time photolithographicprocess including two exposure steps.

In the series of steps described above, the wall structure and thethrough holes electrically connecting to the underlying connectionelectrodes were formed together with the interlayer insulating filmhaving fine uneven surface for imparting diffusion reflectioncharacteristics in reflection display.

Thereafter, for formation of the pixel electrodes, a transparentelectric film (ITO film) was formed on the flat surface of theinterlayer insulating film under predetermined conditions, and areflective electrode film was formed on the uneven surface of theinterlayer insulating film by sputtering. In the patterning for thepixel electrodes, electrode openings (see the openings 214 in FIGS. 3Aand 3B) for fixing/stabilizing the center axes of axisymmetric alignmentwere formed at predetermined positions.

Supports (wall spacers, see the supports 233 in FIGS. 3A and 3B) wereformed at positions of the color filter substrate (counter substrate)corresponding to the shading region (region in which the wall structurewas formed) of the active matrix substrate. The inclined sides of thesupports were inversely tapered with respect to the counter substrate,and the tilt angle (angle formed between the substrate surface and theinclined side) was about 45°. A transparent dielectric layer was formedon the color filter substrate in each reflection region to give a stepfor adjusting the thickness of the liquid crystal layer in thereflection region.

Vertical alignment films were formed on the active matrix substrate andthe color filter substrate under predetermined conditions (No rubbingwas made), and the two substrates were bonded together via a sealingresin. A liquid crystal material having negative dielectric anisotropy(Δn: 0.1 and Δ∈: −4.5) was injected in the space between the twosubstrates and sealed, to obtain a liquid crystal cell. In this example,the thicknesses dt and dr of the liquid crystal layer in thetransmission region and the reflection region were set at 4 μm and 2.1μm, respectively.

The resultant liquid crystal cell was sandwiched between two orthogonalpolarizing plates, and observed. As a result, it was confirmed thatliquid crystal molecules near the supports and the wall structurecontinuously fell along the inclined sides during voltage application,forming axisymmetric liquid crystal domains.

Optical films were placed on the outer surfaces of the liquid crystalcell to obtain an LCD device.

The LCD device of this example had a multilayer structure composed of apolarizing plate (observer side), a quarter wave plate (phase plate 1),a phase plate having negative optical anisotropy (phase plate 2 (NRplate)), the liquid crystal layer (on the upper and lower sides thereof,the color filter substrate and the active matrix substrate wererespectively placed), a phase plate having negative optical anisotropy(phase plate 3 (NR plate)), a quarter wave plate (phase plate 4), and apolarizing plate (backlight side) in the order from the observer side.The upper and lower quarter wave plates (phase plates 1 and 4) wereplaced so that the slower axes thereof were orthogonal to each other,and had a phase difference of 140 nm. The phase plates having negativeoptical anisotropy (phase plates 2 and 3) had a phase difference of 135nm. The two polarizing plates were placed so that the absorption axesthereof were orthogonal to each other.

A drive signal was applied to the thus-obtained LCD device (4V wasapplied across the liquid crystal layer) to evaluate the displaycharacteristics.

The results of the visual angle—contrast characteristics in thetransmission display are shown in FIG. 8. The viewing anglecharacteristics in the transmission display were roughly symmetric inall directions, the range CR>10 was as large as up to ±80°, and thetransmission contrast was as high as 300:1 or more at the front.

As for the characteristics of the reflection display, the reflectanceevaluated with a spectral colorimeter (CM2002 from Minolta Co., Ltd.)was about 8.2% (value in terms of the aperture ratio of 100%) withrespect to a standard diffuse plate as the reference. The contrast valueof the reflection display was 22, which was high compared with the caseof the conventional LCD devices.

The response time for 90% change of the transmittance of the liquidcrystal panel (t_(ON)+t_(OFF) (ms); t_(ON): time required for a changeduring 0V→4V voltage application, t_(OFF): time required for a changeduring voltage 4V→0V) and the grayscale response time for 50% change ofthe transmittance (time required for a change from level 3 to level 5 inthe eight levels of grayscale) were measured and compared betweenExamples 1 and 2. The results are as shown in the following table. Themeasurement temperature was 250 in both cases.

TABLE 1 Response time Grayscale response time (0

 4 V (ms)) (ms) Example 1 35 52 Example 2 30 41

It was confirmed that in the LCD device of Example 2, which had the wallstructure and the electrode openings 214 in addition to the alignmentregulating force of the supports, the axisymmetric alignment was furtherstabilized and the effect of shorting the response time was great.

It was found that in both Examples 1 and 2, the shock resistanceimproved. For example, in a load test (1 kgf/cm²) for liquid crystalpanels, the time required to recover the original alignment fromonce-disturbed alignment due to application of a load was five minutesor less, proving that the LCDs had sufficient alignment recoverycapability. The reason is presumably that in both examples the densityof placement of the supports is higher than in conventional LCDS. InExample 2, naturally, the wall structure and the openings alsocontribute to this capability.

Comparative Example 1

A liquid crystal display panel, having the same construction as the LCDdevice shown in FIGS. 3A and 3B except that the openings and the wallstructure were omitted and the supports formed in Example 1 were used asthe supports, was fabricated, and horizontal alignment films were used,to provide an ECB mode homogeneously aligned liquid crystal panel. Aliquid crystal material having positive dielectric anisotropy (Δn: 0.07,Δ∈: 8.5) was used. The thickness dt and dr of the liquid crystal layerin the transmission regions and the reflection regions were 4.3 μm and2.3 μm, respectively (dr=0.53 dt).

Optical films each formed of a plurality of optical layers including apolarizing plate and a phase plate such as a quarter wave plate wereplaced on both surfaces of the liquid crystal display panel, to obtainan LCD device.

A drive signal was applied to the resultant LCD device (4V was appliedacross the liquid crystal layer) to evaluate the display characteristicsby the same evaluation method as that described.

As the viewing angle characteristics in the transmission display, therange of CR>10 was up to ±30° and reverse gradation was eminent. Thetransmission contrast was 140:1. As for the characteristics of thereflection display, the reflectance was about 9.3% (value in terms ofthe aperture ratio of 100%) with respect to a standard diffuse plate asthe reference. The contrast value of the reflection display was 8, andthe display image was white-blurred and low in contrast compared withthe LCD devices of the examples according to the first aspect of thevertical alignment mode.

A load test was also conducted to examine the shock resistance under thesame conditions as those for the above examples. As a result, analignment disturbance was recognized after the test, indicating that theLCD device of the comparative example was poor in shock resistancecompared with the above examples.

As described above, in the LCD devices according to the first aspect ofthe present invention, in which the vertical alignment mode was appliedto transmission display and reflection display, a good contrast ratiowas obtained both in the transmission display and the reflectiondisplay, compared with the conventional homogeneously aligned LCDdevices and the conventionally known technologies. Also, since thesupports (wall spacers) for defining the thickness of the liquid crystallayer are used for alignment regulation, no additional step forproviding an alignment regulating structure is necessary. Since thesupports are regularly provided at a sufficiently high density, theshock resistance improves.

In addition, by placing the structures for controlling the alignment ofliquid crystal domains (the wall structure and the openings) only on onesubstrate (in the illustrated examples, on the active matrix substrate),the alignment of liquid crystal domains can be further stabilized, andthus viewing angle characteristics wide in all directions can beattained. Moreover, since the position of the center axes of the domainscan be fixed/stabilized with the openings, the effect of improving theuniformity of display at slanting visual angles can be obtained.

Next, the construction and operation of LCD devices according to thesecond aspect of the present invention will be described.

In the LCD devices according to the second aspect of the presentinvention, at least one pixel region is divided into a plurality ofsub-pixel regions with a dielectric structure (protrusions). Liquidcrystal molecules in the liquid crystal layer in each sub-pixel regionare axisymmetrically aligned during voltage application. In thefollowing description, the region corresponding to each of a pluralityof axisymmetrically aligned domains formed in each pixel is called asthe “sub-pixel region”.

In a preferred embodiment, a wall structure substantially surroundingeach pixel region is formed in a shading region. The dielectricprotrusions and the wall structure may be formed integrally, or may beformed of a same dielectric material, or otherwise may be formed ofdifferent patterning materials.

One object of the second aspect of the present invention is to suppressdisplay failure due to poor alignment occurring after disturbance inalignment with pressing of the liquid crystal panel and improve thedisplay, and this object is attained by separating the regions of liquidcrystal domains from each other with the dielectric protrusions and thewall structure. To state specifically, in the event of a collapse ofaxisymmetric alignment with pressing of the display screen, stabilizingthe alignment is attempted from the peripheries of the divided liquidcrystal domains with the action of the wall structure and the dielectricprotrusions formed around the liquid crystal domains. In other words,the wall structure and the dielectric protrusions impart the force ofrecovering the disturbed alignment to the liquid crystal domains.

(Operation Principle)

The reason why the LCD device having a vertically aligned liquid crystallayer of the present invention has excellent wide viewing anglecharacteristics will be described with reference to FIGS. 9A and 9B.FIGS. 9A and 9B are views for demonstrating how the alignment regulatingforce of dielectric protrusions 23 and a wall structure formed around apixel electrode 6 act, in which the aligned states of liquid crystalmolecules during non-voltage application (FIG. 9A) and during voltageapplication (FIG. 9B) are diagrammatically shown. The state shown inFIG. 9B is for display of a grayscale level.

The LCD device shown in FIGS. 9A and 9B includes an insulating film (notshown), a pixel electrode 6 having the dielectric protrusions 23 and awall structure, and a vertical alignment film 22 formed in this order ona transparent substrate 1. The LCD device also includes a color filterlayer (not shown), a counter electrode 19 and an alignment film 32formed in this order on another transparent substrate 17. A liquidcrystal layer 20 interposed between the two substrates includes liquidcrystal molecules 21 having negative dielectric anisotropy. Although notshown in FIGS. 9A and 9B, the vertical alignment film 22 also covers thedielectric protrusions 23.

As shown in FIG. 9A, during non-voltage application, the liquid crystalmolecules 21 are aligned roughly vertical to the substrate surface withthe alignment regulating force of the vertical alignment films 22 and32. During voltage application, as shown in FIG. 9B, the liquid crystalmolecules 21 having negative dielectric anisotropy attempt to make theirmajor axes vertical to electric lines of force, and tilt in directionsalong equipotential lines (parallel to equipotential lines) affected byan electric field. Thus, an axisymmetrically aligned domain is formed asa result of the alignment of the liquid crystal molecules 21 tilting inthe inclined direction of the electric field and also the alignment ofthe liquid crystal molecules tilting near the side steps of thedielectric protrusions 23 or the side steps of the wall structure. Inthe axisymmetrically aligned domain, the liquid crystal directors pointto all azimuth directions (directions in the substrate plane), and thusthe resultant LCD exhibits excellent viewing angle characteristics.

In this embodiment, the wall structure and the dielectric protrusionsare provided around at least part of each liquid crystal domain. Thisstabilizes the tilting of liquid crystal molecules on the sides of thewall structure and the dielectric protrusions, and also serves to reducepoor alignment due to a disturbance in alignment after pressing of thepanel plane. Specifically, the alignment of liquid crystal molecules inthe liquid crystal domain is less disturbed and the disturbedaxisymmetrically aligned domain is effectively recovered, compared withthe conventional methods in which the electroclinic direction of liquidcrystal molecules is regulated with the action of an electric fieldgenerated when a voltage is applied to a slit electrode. As a result,display roughness can be greatly improved.

The wall structure and the dielectric protrusions in this embodiment areprovided at predetermined positions by regularly patterning aphotosensitive resin via photolithography. In this embodiment, the wallstructure and the dielectric protrusions may be formed of a samematerial, or may be formed of different materials as required.

In an embodiment according to the second aspect of the presentinvention, each of a plurality of pixel regions is defined by a firstelectrode (for example, a pixel electrode) and a second electrode. Atleast one pixel region, among the plurality of pixel regions, is dividedinto a plurality of sub-pixel regions with regularly arranged dielectricprotrusions and a wall structure formed in a shading region. The tiltdirection of liquid crystal molecules in a portion of the liquid crystallayer (liquid crystal domain) in each sub-pixel region is regulated withthe side steps of the dielectric protrusions and the side steps of thewall structure during voltage application, to assume axisymmetricalignment. With the existence of the dielectric protrusions and the wallstructure surrounding at least part of the liquid crystal domain, thealigned state can be suppressed from changing when the panel plane ispressed. Also, degradation in display quality that may otherwise occurdue to variations in axial position and changes in axisymmetricalignment can be prevented. In particular, by providing the wallstructure in a shading region, decrease in pixel effective apertureratio can be prevented. Light leakage that may occur if the wallstructure is provided in the pixel region can also be prevented, andthis can suppress decrease in contrast ratio. Thus, the display qualitywill not be sacrificed.

In another embodiment, the first electrode and/or the second electrodehave openings regularly provided at predetermined positions in thesub-pixel region. Since the opening serves to fix the position of thecenter axis of axisymmetric alignment, the axisymmetric alignment ismore stabilized.

In application of the present invention to a transflective LCD device,the dielectric protrusions may be placed near the boundary between atransmission region and a reflection region. This separates liquidcrystal domains in the transmission region and the reflection regionsfrom each other, and thus the aligned state can be stabilized moreeasily.

An LCD device of an embodiment according to the second aspect of thepresent invention will be described specifically with reference to therelevant drawings. Although an active matrix LCD device using thin filmtransistors (TFTs) will be exemplified in this embodiment, the presentinvention is not limited to this type, but is also applicable to MIM(metal insulator metal) active matrix LCD devices and simple matrix LCDdevices. Also, although a transmissive LCD device and a transflectiveLCD device (also called transmissive/reflective LCD device) areexemplified in this embodiment, the present invention is not limited tothese types, but is also applicable to reflective LCD devices andsemitransparent LCD devices using a semitransparent film such as a halfmirror.

As used herein, the region of the LCD device corresponding to the“pixel” as the minimum unit of display is called a “pixel region”. Incolor LCD devices, three pixels of red, green and blue, for example,constitute one “picture element”. In active matrix LCD devices, thepixel region is defined by a pixel electrode and the portion of thecounter electrode facing the pixel electrode. In simple matrix LCDdevices, the pixel region is defined by the portion of a stripe-shapedcolumn electrode and the portion of a row electrode running orthogonalto the column electrode that cross each other. In LCD devices having ashading-layer such as a black matrix, the pixel region strictlycorresponds to the portion corresponding to an opening of the blackmatrix out of the region across which a voltage is applied depending onthe display state.

(Transmissive LCD Device)

A transmissive LCD device 300 of an embodiment of the present inventionwill be described with reference to FIGS. 10A and 10B. FIGS. 10A and 10Bdiagrammatically show one pixel of the transmissive LCD device 300, inwhich FIG. 10A is a plan view as is viewed in the direction normal tothe substrate plane and FIG. 10B is a cross-sectional view taken alongline 10B-10B′ in FIG. 10A.

The LCD device 300 includes a transparent substrate (for example, aglass substrate) 310 a, a transparent substrate 310 b placed to face thetransparent substrate 310 a, and a vertically aligned liquid crystallayer 320 interposed between the transparent substrates 310 a and 310 b.Vertical alignment films (not shown) are formed on the surfaces of thesubstrates 310 a and 310 b facing the liquid crystal layer 320. Duringnon-voltage application, therefore, liquid crystal molecules in theliquid crystal layer 320 are aligned roughly vertical to the surfaces ofthe vertical alignment films. The liquid crystal layer 320 includes anematic liquid crystal material having negative dielectric anisotropyand also includes a chiral agent as required.

The LCD device 300 further includes pixel electrodes 311 formed on thetransparent substrate 310 a and a counter electrode 331 formed on thetransparent substrate 310 b. Each pixel electrode 311, the counterelectrode 331 and the liquid crystal layer 320 interposed between theseelectrodes define a pixel. In the illustrated example, both the pixelelectrodes 311 and the counter electrode 331 are formed of a transparentconductive film such as an indium tin oxide (ITO) film, for example.Typically, color filters 330 (the entire of the plurality of colorfilters of plural colors may also be called a color filter layer 330)provided for the respective pixels, as well as a black matrix (shadinglayer) 332 formed in the gaps between the adjacent color filters 330,are formed on the surface of the transparent substrate 310 b facing theliquid crystal layer 320, and the counter electrode 331 is formed on thecolor filters 330 and the black matrix 332. Alternatively, the colorfilters 330 and the black matrix 332 may be formed on the counterelectrode 331 (on the surface thereof facing the liquid crystal layer320).

In this embodiment, a pixel region in the shape of a rectangle having apair of longer sides and a pair of shorter sides as is viewed from top(in the direction normal to the substrate plane) is defined by the pixelelectrode 311 and the counter electrode 331. A wall structure 315substantially surrounding the pixel region and a pair of dielectricprotrusions 316 are formed around the pixel region on the transparentsubstrate 310 a. The pair of dielectric protrusions 316 are formed inroughly the centers of the longer sides of the pixel region in line witheach other in the shorter-side direction (direction of extension of theshorter sides), and extend from near the longer sides of the pixelregion (from the inner sides of the wall structure 315) in the directioncloser to each other. The length of the dielectric protrusions 316 (inthe shorter-side direction) is about one-third or less of the length ofthe shorter sides of the pixel region, although the length is preferably5 μm or more. If the length of the dielectric protrusions 316 is lessthan 5 μm, the dividing effect of the dielectric protrusions 316 issmall and thus the alignment regulating force may decrease. The heightof the wall structure 315 and the dielectric protrusions 316 ispreferably equal to or less than a half of the cell thickness (thedistance between the substrates 310 a and 310 b or the thickness of theliquid crystal layer 320) in consideration of easiness of injection ofthe liquid crystal material. If the height of the wall structure 315 andthe dielectric protrusions 316 is less than 0.5 μm, the alignmentregulating force decreases and this may decrease the display contrastratio. Hence, the height of the wall structure 315 and the dielectricprotrusions 316 is preferably 0.5 μm or more. The pixel region isdivided into two sub-pixel regions with the wall structure 315 and thepair of dielectric protrusions 316. In other words, the liquid crystallayer 320 in the pixel region is divided into two liquid crystaldomains.

In this embodiment, the pixel electrode 311 has two openings 314 formedat predetermined positions. Specifically, each opening 314 is formedroughly in the center of each sub-pixel region. When a predeterminedvoltage is applied across the liquid crystal layer 320, two liquidcrystal domains (sub-pixel regions) each exhibiting axisymmetricalignment are formed. The center axis of the axisymmetric alignment ofeach of the liquid crystal domains is located in or near the opening314. In other words, the opening 314 formed in the pixel electrode 311acts to fix the position of the center axis of the axisymmetricalignment.

Moreover, side steps 316 a of the dielectric protrusions 316 and sidesteps 315 a of the wall structure 315 serve to define the tiltdirections of the liquid crystal molecules, and also serve to formstable axisymmetrically aligned domains in the sub-pixel regions. Whenthe dielectric protrusions 316 are formed in the pixel region, shadingportions are formed to correspond to at least the regions of thedielectric protrusions 316, preferably to the regions of the dielectricprotrusions 316 and their neighboring regions. Such shading portions maynot necessarily be part of the black matrix, but may be elements that donot transmit light such as part of a storage capacitance line.Otherwise, to stabilize the axisymmetrically aligned domains, cuts 313may be formed in the pixel electrode 311 to surround the dielectricprotrusions 316. With such cuts, the electroclinic effect with aninclined electric field during voltage application can also be used.

The shape of the openings 314 formed for fixing of the center axes ofthe axisymmetrically aligned domains is preferably circular asillustrated, but is not limited to this. To exert roughly equalalignment regulating force in all directions, however, the shape ispreferably a polygon having four or more sides and more preferably aregular polygon.

The LCD device 300 of this embodiment has a shading region between theadjacent pixels. In other words, the pixel region is surrounded by ashading region as is viewed from top. The wall structure 315 is placedon the transparent substrate 310 a in the shading region. The shadingregion as used herein refers to a region that does not contribute todisplay, formed around the pixel electrode 311 on the transparentsubstrate 310 a. For example, the shading region is a region shaded fromlight due to the presence of TFTs, gate signal lines and source signallines formed on the transparent substrate 310 a, or a region shaded fromlight due to the presence of the black matrix formed on the transparentsubstrate 310 b. Since the shading region does not contribute todisplay, the wall structure 315 formed in the shading region is freefrom adversely affecting the display.

The wall structure 315 in this embodiment is shown as a continuous wallsurrounding the pixel region, but is not limited to this. The wallstructure 315 is just required to substantially surround the pixelregion, and may be composed of a plurality of separate walls, forexample. The wall structure 315, which defines liquid crystal domains (apixel region), should preferably have a length of some extent. Forexample, when the wall structure 315 is composed of a plurality ofwalls, each wall is preferably longer than the gap between the adjacentwalls.

Supports 333 for defining the thickness dt of the liquid crystal layer320 (also called the cell gap) are preferably formed in the shadingregion (in the illustrated example, the region defined by the blackmatrix 332) to avoid degradation in display quality due to the supports.Although the supports 333 are formed on the wall structure 315 providedin the shading region in the example in FIG. 10B, the supports 333 maybe formed on either transparent substrate 310 a or 310 b. In the case offorming the supports 333 on the wall structure 315, setting is made sothat the sum of the height of the wall structure 315 and the height ofthe supports 333 is equal to the thickness of the liquid crystal layer320. If the supports 333 are formed in a region having no wall structure315, setting is made so that the height of the supports 333 is equal tothe thickness dt of the liquid crystal layer 320.

The LCD device 300 of this embodiment can be fabricated using a generaltechnique such as photolithography. For example, the wall structure 315,the dielectric protrusions 316 and the supports 333 can be formed in thefollowing procedure. First, TFTs, gate signal lines, source signallines, pixel electrodes 311 having the openings 314 and the like areformed on the substrate 310 a by photolithography. A photosensitiveresin film is then formed on the resultant substrate, and patterned toform the wall structure 315 and the dielectric protrusions 316. Thesupports 333 are then formed by photolithography using a photosensitiveresin. Thereafter, a vertical alignment film (not shown) is formedcovering the pixel electrodes 311, the wall structure 315 and thedielectric protrusions 316.

In the LCD device 300 of this embodiment, when a predetermined voltage(voltage equal to or higher than a threshold voltage) is applied betweenthe pixel electrode 311 and the counter electrode 331, twoaxisymmetrically aligned domains of which the center axes are stabilizedin or near the two openings 314 are formed. The pair of dielectricprotrusions 316 provided in the center portion of the pixel electrode311 in the length direction define the directions of tilt of the liquidcrystal molecules in the two separated liquid crystal domains adjacentto each other in the length direction. The wall structure 315 is formedaround the pixel electrode 311 and near the dielectric protrusions 316.The directions of tilt of the liquid crystal molecules near the wallstructure 315 in the pixel region are defined with the synergisticeffect of the dielectric protrusions 316 and the wall structure 315. Thealignment regulating forces of the openings 314, the dielectricprotrusions 316 and the wall structure 315 are considered to actcooperatively, to thereby stabilize the alignment of the liquid crystaldomain.

On the surface of the transparent substrate 310 a facing the liquidcrystal layer 320, provided are active elements such as TFTs and circuitelements such as gate signal lines and source signal lines connected toTFTs (all of these elements are not shown). Herein, the transparentsubstrate 310 a, together with the circuit elements and the pixelelectrodes 311, the wall structure 315, the supports 333, the alignmentfilm and the like described above formed on the transparent substrate310 a, are collectively called an active matrix substrate in some cases.Likewise, the transparent substrate 310 b, together with the colorfilter layer 330, the black matrix 332, the counter electrode 331, thealignment film and the like formed on the transparent substrate 310 b,are collectively called a counter substrate or a color filter substratein some cases.

Although omitted in the above description, the LCD device 300 furtherincludes a pair of polarizing plates placed to face each other via thetransparent substrates 310 a and 310 b. The polarizing plates aretypically placed so that their transmission axes are orthogonal to eachother. The LCD device 300 may further include a biaxial opticalanisotropic medium layer and/or a uniaxial optical anisotropic mediumlayer between the transparent substrate 310 a and one of the pair ofpolarizing plates and/or between the transparent substrate 310 b and theother polarizing plate, as will be described later.

(Transflective LCD Device)

A transflective LCD device 400 of an embodiment of the present inventionwill be described with reference to FIGS. 11A and 11B. FIGS. 11A and 11Bdiagrammatically show one pixel of the transflective LCD device 400, inwhich FIG. 11A is a plan view as is viewed in the direction normal tothe substrate plane and FIG. 11B is a cross-sectional view taken alongline 11B-11B′ in FIG. 11A.

The LCD device 400 includes a transparent substrate (for example, aglass substrate) 410 a, a transparent substrate 410 b placed to face thetransparent substrate 410 a, and a vertically aligned liquid crystallayer 420 interposed between the transparent substrates 410 a and 410 b.Vertical alignment films (not shown) are formed on the surfaces of thesubstrates 410 a and 410 b facing the liquid crystal layer 420. Duringnon-voltage application, therefore, liquid crystal molecules in theliquid crystal layer 420 are aligned roughly vertical to the surfaces ofthe vertical alignment films. The liquid crystal layer 420 includes anematic liquid crystal material having negative dielectric anisotropyand also includes a chiral agent as required.

The LCD device 400 further includes pixel electrodes 411 formed on thetransparent substrate 410 a and a counter electrode 431 formed on thetransparent substrate 410 b. Each pixel electrode 411, the counterelectrode 431 and the liquid crystal layer 420 interposed between theseelectrodes define a pixel. Circuit elements such as TFTs are formed onthe transparent substrate 410 a as will be described later. Herein, thetransparent substrate 410 a and the components formed thereon arecollectively called an active matrix substrate 410 a in some cases.

Typically, color filters 430 (the entire of the plurality of colorfilters of plural colors may also be called a color filter layer 430)provided for the respective pixels, as well as a black matrix (shadinglayer) 432 provided in the gaps between the adjacent color filters 430,are formed on the surface of the transparent substrate 410 b facing theliquid crystal layer 420, and the counter electrode 431 is formed on thecolor filters 430 and the black matrix 432. Alternatively, the colorfilters 430 and the black matrix 432 may be formed on the counterelectrode 431 (on the surface thereof facing the liquid crystal layer420). Herein, the transparent substrate 410 b and the components formedthereon are collectively called a counter substrate (color filtersubstrate) 410 b in some cases.

In this embodiment, each pixel electrode 411 includes a transparentelectrode 411 a formed of a transparent conductive film (for example, anITO film) and a reflective electrode 411 b formed of a metal film (forexample, an Al layer, an alloy layer including Al, and a layered filmincluding any of these layers). Having such a pixel electrode, eachpixel region includes a transmission region A defined by the transparentelectrode 411 a and a reflection region B defined by the reflectiveelectrode 411 b, to provide display in the transmission mode and displayin the reflection mode, respectively.

In this embodiment, a pixel region in the shape of a rectangle having apair of longer sides and a pair of shorter sides as is viewed from topis defined by the pixel electrode 411 and the counter electrode 431. Awall structure 415 substantially surrounding the pixel region and twopairs of dielectric protrusions 416 and 417 are formed around the pixelregion on the transparent substrate 410 a. The two pairs of dielectricprotrusions 416 and 417 are formed at positions trisecting the longersides of the pixel region each in line with each other in theshorter-side direction (direction of extension of the shorter sides),and extend from near the longer sides of the pixel region (from theinner sides of the wall structure 415) in the direction closer to eachother. As in the LCD device 300, the wall structure 415 substantiallysurrounding the pixel region is formed around the pixel region on thetransparent substrate 410 a. The length of the dielectric protrusions416 and 417, and the heights of the dielectric protrusions and the wallstructure 415 are as described in relation to the LCD device 300. Thepixel region is divided into three sub-pixel regions with the wallstructure 415 and the two pairs of dielectric protrusions 416 and 417.In other words, the liquid crystal layer 420 in the pixel region isdivided into three liquid crystal domains. Two out of the threesub-pixel regions are transmission regions A and one is a reflectionregion B. In this embodiment, the two transmission regions A sandwichone sub-pixel region in the length direction as is viewed from top.

In this embodiment, the pixel region 411 has three openings 414 atpredetermined positions (two in the transmission regions A and one inthe reflection region B). Specifically, each opening 414 is formedroughly in the center of each sub-pixel region. When a predeterminedvoltage is applied across the liquid crystal layer 420, three liquidcrystal domains (sub-pixel regions) each exhibiting axisymmetricalignment are formed. The center axis of the axisymmetric alignment ofeach of the liquid crystal domains is located in or near the opening414. In other words, the opening 414 formed in the pixel electrode 411acts to fix the position of the center axis of the axisymmetricalignment.

Moreover, side steps 416 a and 417 a of the dielectric protrusions 416and 417 and side steps 415 a of the wall structure 415 serve to definethe tilt directions of the liquid crystal molecules, and also serve toform stable axisymmetrically aligned domains in the sub-pixel regions.When the dielectric protrusions 416 and 417 are formed in the pixelregion, shading portions are formed to correspond to at least theregions of the dielectric protrusions 416 and 417, preferably to theregions of the dielectric protrusions 416 and 417 and their neighboringregions. Such shading portions may not necessarily be part of the blackmatrix, but may be elements that do not transmit light such as part ofstorage capacitance lines. Otherwise, to stabilize the axisymmetricallyaligned domains, cuts (not shown) may be formed in the pixel electrode411 to surround the dielectric protrusions 416 and 417. With such cuts,the electroclinic effect with an inclined electric field during voltageapplication can also be used.

In this embodiment, the transmission region A and the reflection regionB are arranged alternately in the display region of one pixel to formthe pixel electrode. Also, two pairs of dielectric protrusions 416 and417 are provided in the pixel division portions near the boundariesbetween the transmission region A and the reflection region B to formliquid crystal division regions. As a result, two liquid crystal domainsare formed in the transmission regions A and one liquid crystal domainis formed in the reflection region B. Note however that this embodimentis merely illustrative and the present invention is not limited to this.Preferably, the shape of the liquid crystal domains is roughly a squarefrom the standpoint of the viewing angle characteristics and thestability of alignment.

FIGS. 12A to 12C are diagrammatic views of axisymmetrically alignedstates observed in the embodiment of the present invention and aconventional LCD device, in which FIG. 12A shows the alignment of liquidcrystal domains in the steady state before pressing of the displayplane, FIG. 12B shows the alignment after pressing in a conventionalpixel-divided panel, and FIG. 12C shows the alignment after pressing inthe pixel-divided panel of the embodiment of the present invention. Theellipses in FIG. 12C indicate existence of dielectric protrusions.

In this embodiment, the transmission region A and the reflection regionB are arranged alternately (to be adjacent to each other), and theliquid crystal layer in the pixel region is divided into three with thedielectric protrusions and the wall structure (not shown) to form threeliquid crystal domains. This enables uniform division into the liquidcrystal domains with the dielectric protrusions and the wall structure,and therefore when the panel plane is pressed, a temporarily disturbedaxisymmetrically aligned state is prevented from appearing in theadjacent pixels and is restored to the original good axisymmetricallyaligned state. Thus, compared with the case of FIG. 12B in which onepixel region is divided into three in the arrangement of transmissionregion/transmission region/reflection region having transmission regionssuccessively, it has been confirmed that a temporarily disturbedaxisymmetrically aligned state is immediately restored to the originalstable axisymmetric alignment.

The LCD device 400 of this embodiment has a shading region between theadjacent pixels. In other words, the pixel region is surrounded by ashading region as is viewed from top. The wall structure 415 is placedon the transparent substrate 410 a in the shading region. Since theshading region does not contribute to display, the wall structure 415formed in the shading region is free from adversely affecting thedisplay.

The wall structure 415 in this embodiment is shown as a continuous wallsurrounding the pixel region, but is not limited to this. The wallstructure 415 is just required to substantially surround the pixelregion, and may be composed of a plurality of separate walls, forexample. The wall structure 415, which defines liquid crystal domains (apixel region), should preferably have a length of some extent. Forexample, when the wall structure 415 is composed of a plurality ofwalls, each wall is preferably longer than the gap between the adjacentwalls.

Supports 433 for defining the thickness dt of the liquid crystal layer420 (also called the cell gap) are preferably formed in the shadingregion (in the illustrated example, the region defined by the blackmatrix 432) to avoid degradation in display quality due to the supports.Although the supports 433 are formed on the wall structure 415 providedin the shading region as shown in FIG. 11B, the supports 433 may beformed on either transparent substrate 410 a or 410 b. In the case offorming the supports 433 on the wall structure 415, setting is made sothat the sum of the height of the wall structure 415 and the height ofthe supports 433 is equal to the thickness of the liquid crystal layer420. If the supports 433 are formed in a region having no wall structure415, setting is made so that the height of the supports 433 is equal tothe thickness dt of the liquid crystal layer 420.

In the LCD device 400 of this embodiment, when a predetermined voltage(voltage equal to or higher than a threshold voltage) is applied betweenthe pixel electrode 411 and the counter electrode 431, threeaxisymmetrically aligned domains of which the center axes are stabilizedin or near the three openings 414 are formed. The directions of tilt ofthe liquid crystal molecules are defined in the regions partitioned withthe dielectric protrusions 416 and 417 and the wall structure 415 formedaround the pixel electrode 411, forming liquid crystal domains.

Next, a preferred construction specific to the transflective LCD device400 permitting both the transmission-mode display and thereflection-mode display will be described. While light used for displaypasses through the liquid crystal layer 420 once in thetransmission-mode display, it passes through the liquid crystal layer420 twice in the reflection-mode display. Accordingly, asdiagrammatically shown in FIG. 11B, the thickness dt of the liquidcrystal layer 420 in the transmission region A is preferably set roughlydouble the thickness dr of the liquid crystal layer 420 in thereflection region B. By setting in this way, the retardation given tothe light by the liquid crystal layer 420 can be roughly the same inboth display modes. Most preferably, dr 0.5 dt should be satisfied, butgood display is secured in both display modes as long as 0.3 dt<dr<0.7dt is satisfied. Naturally, dt=dr may be satisfied depending on the use.

In the LCD device 400, a transparent dielectric layer 434 is provided onthe glass substrate 410 b only in the reflection region B to make thethickness of the liquid crystal layer 420 in the reflection region Bsmaller than that in the transmission region A. This constructioneliminates the necessity of providing a step by forming an insulatingfilm and the like under the reflective electrode 411 b, and thus has theadvantage of simplifying the fabrication of the active matrix substrate410 a. If the reflective electrode 411 b is formed on such an insultingfilm provided to give a step for adjusting the thickness of the liquidcrystal layer 420, light used for transmission display will be shadedwith the reflective electrode covering a slope (tapered face) of theinsulating film, and light reflected from the reflective electrodeformed on a slope of the insulating film will repeat internalreflection, failing to be effectively used for reflection display. Byadopting the construction described above, occurrence of such problemsis prevented, and thus the light use efficiency can be improved.

If the transparent dielectric layer 434 is provided with a function ofscattering light (diffuse reflection function), good white display closeto paper white can be realized without the necessity of providing thereflective electrode 411 b with the diffuse reflection function. Suchwhite display close to paper white can also be realized by making thesurface of the reflective electrode 411 b uneven, and in this case, nolight scattering function is necessary for the transparent dielectriclayer 434. However, the uneven surface may fail to stabilize theposition of the center axis of the axisymmetric alignment depending onthe shape of the uneven surface. On the contrary, by combining thetransparent dielectric layer 434 having the light scattering functionand the reflective electrode 411 b having a flat surface, the positionof the center axis can be stabilized with the opening 414 formed in thereflective electrode 411 b more reliably. The following method, forexample, may be adopted to provide the transparent dielectric layer 434with the light scattering function. Ultrafine particles such as titaniumoxide particles are dispersed in a transparent resin. The resultantresin is applied to a support such as a polyimide film, to form ascattering layer having a light scattering function. The scatteringcharacteristics can be changed by changing the particle density, theparticle size, the thickness of the scattering layer, the refractiveindex of the resin and the like. As another method, thin films differentin refractive index may be formed one on top of another to form a lightscattering layer.

Note that in the case of making the surface of the reflective electrode411 b uneven to provide the reflective electrode 411 b with the diffusereflection function, the uneven shape is preferably a continuous waveshape to prevent occurrence of an interference color, and such a shapeis preferably set to allow stabilization of the center axis of theaxisymmetric alignment.

While light used for display passes through the color filter layer 430once in the transmission mode, it passes through the color filter layer430 twice in the reflection mode. Accordingly, if the color filter layer430 has the same optical density both in the transmission region A andthe reflection region B, the color purity and/or the luminance maydecrease in the reflection mode. To suppress occurrence of this problem,the optical density of the color filter layer in the reflection regionis preferably made lower than that in the transmission region. Theoptical density as used herein is a characteristic value characterizingthe color filter layer. For example, the optical density can be reducedby reducing the thickness of the color filter layer. Otherwise, theoptical density can be reduced by reducing the density of a pigmentadded, for example, while keeping the thickness of the color filterlayer unchanged.

In the transflective LCD device of this embodiment, also, the activematrix substrate described with reference to FIGS. 4 and 5 can besuitably used.

As described above, the LCD device 400 shown in FIGS. 11A and 11Bexhibits the effect of stabilizing the alignment of liquid crystalmolecules sufficiently with a comparatively simple construction in whichthe alignment control structure for axisymmetric alignment (the openings414 formed in the pixel electrode 411, the dielectric protrusions 416and 417 and the wall structure 415) is formed on only the substrate 410a. Also, with the placement of the transparent dielectric layer 434and/or the color filter layer 430 in the manner described above, thedisplay brightness and color purity in both the transmission mode andthe reflection mode can be improved.

The specific construction of the transflective LCD device of thisembodiment can be that described above with reference to FIG. 7.

(Relationship Between the Thicknesses dt and dr of the Liquid CrystalLayer in the Transmission Region and the Reflection Region)

FIG. 13 is a graph showing the voltage-reflectance (transmittance) ofthe transmission region and the reflection region in the LCD device ofthis embodiment. As shown in FIG. 13, the thicknesses dt and dr in thetransmission region and the reflection region preferably satisfy 0.3dt<dr<0.7 dt, more preferably 0.4 dt<dr<0.6 dt. If the thickness dr ofthe liquid crystal layer in the reflection region is smaller than thelower limit, the reflectance will be 50% or less of the maximumreflectance, failing to provide sufficiently high reflectance. If thethickness dr is greater than the upper limit, a maximum of thereflectance in the voltage-reflectance characteristics exists at a drivevoltage different from that in the transmission display. Also, thereflectance tends to be relatively low at a white display voltageoptimal for the transmission display. The reflectance is as low as 50%or less of the maximum reflectance in some cases, failing to providesufficiently high reflectance. Since the optical length in the liquidcrystal layer in the reflection region is about twice as large as thatin the transmission region, the birefringence anisotropy (Δn) of theliquid crystal material and the panel cell thickness design are veryimportant when the same optical design is made for both the transmissionregion A and the reflection region B. This also applies to thetransflective LCD device according to the first aspect of the presentinvention.

Example

Specific characteristics of the transflective LCD device of thisembodiment will be described.

An LCD device having the construction shown in FIG. 7 was fabricated. Asthe liquid crystal cell 50, one having the same construction as the LCDdevice 400 shown in FIGS. 11A and 11B was used. A transparent dielectriclayer having no light scattering function was formed as the transparentdielectric layer 434, and a resin layer having a continuous unevensurface was formed under the reflective electrode 411 b, to adjust thediffuse reflection characteristics in the reflection display.

The pixel region in this example is divided into three sub-pixel regionswith the wall structure and the dielectric protrusions, and has atransmission region, a reflection region and a transmission region inthis order in the length direction. The wall structure is formed on ashading layer formed in the non-display region (region other than thepixel region). Thus, an axisymmetrically aligned domain is formed ineach region during voltage application.

The vertical alignment films were formed using a known alignment filmmaterial by a known method. No rubbing was made. A liquid crystalmaterial having negative dielectric anisotropy (Δn: 0.1 and Δ∈: −4.5)was used. In this example, the thicknesses dt and dr of the liquidcrystal layer in the transmission region and the reflection region wereset at 4 μm and 2.2 μm, respectively (dr=0.55 dt).

The LCD device of this example had a multilayer structure composed of apolarizing plate (observer side), a quarter wave plate (phase plate 1),a phase plate having negative optical anisotropy (phase plate 2 (NRplate)), the liquid crystal layer (on the upper and lower sides thereof,the color filter substrate and the active matrix substrate wererespectively placed), a phase plate having negative optical anisotropy(phase plate 3 (NR plate)), a quarter wave plate (phase plate 4), and apolarizing plate (backlight side) in the order from the observer side.The upper and lower quarter wave plates (phase plates 1 and 4) wereplaced so that the slower axes thereof were orthogonal to each other,and had a phase difference of 140 nm. The phase plates having negativeoptical anisotropy (phase plates 2 and 3) had a phase difference of 135nm. The two polarizing plates were placed so that the absorption axesthereof were orthogonal to each other.

A drive signal was applied to the thus-obtained LCD device (4V wasapplied across the liquid crystal layer) to evaluate the displaycharacteristics. The visual angle—contrast characteristics in thetransmission display were substantially the same as those shown in FIG.8. The viewing angle characteristics in the transmission display wereroughly symmetric in all directions, the range CR>10 was as large as upto ±80°, and the transmission contrast was as high as 300:1 or more atthe front.

As for the characteristics of the reflection display, the spectralreflectance evaluated with a spectral calorimeter (CM2002 from MinoltaCo., Ltd.) was about 8.1% (value in terms of the aperture ratio of 100%)with respect to a standard diffuse plate as the reference. The contrastvalue of the reflection display was 20, which was high compared with thecase of the conventional LCD devices.

Comparative Example

In the LCD device shown in FIGS. 11A and 11B, one pixel region wasdivided into a transmission region, a transmission region and areflection region in this order using only slits (electrode openings)without placing any wall structure or dielectric protrusions dividingthe pixel region. In other words, the pixel region was divided intothree using only the action of an electric field generated at theelectrode openings during voltage application.

An LCD device having the above construction was fabricated under thesame conditions of the liquid crystal layer as those in the aboveexample, and the same panel evaluation as that described above wasconducted for this comparative example. As a result, as for the displaycharacteristics such as the contrast, roughly the same characteristicsas those of the above example were obtained.

(Evaluation)

The display roughness, the grayscale response characteristics and thedisplay quality after panel pressing were compared between the LCDdevices of the above example and comparative example. The roughness indisplay of a grayscale level (level 2 in eight levels of grayscale)observed in an oblique direction was visually evaluated. As a result,while no roughness was recognized in the example of the presentinvention, roughness was recognized in the display of the grayscalelevel at a slanting visual angle in the LCD device of the comparativeexample using only slits for pixel division.

The LCD devices were observed with an optical microscope of which thepolarizing axes were set orthogonal to each other. As a result, whileaxisymmetrically aligned domains of which the center axes were inposition uniformly in the example of the present invention, there weresome liquid crystal domains of which the center axes were deviated fromthe center positions (openings) of the sub-pixel regions in thecomparative example. This variation in the position of the center axiswas confirmed to be a main cause of the roughness.

The grayscale response time (time required for a change from level 3 tolevel 5 in the eight levels of grayscale) was 38 msec in the example ofthe present invention and 65 msec in the comparative example. It wastherefore confirmed that the response time in grayscale display could beshortened in the LCD device of the present invention in which the pixelregion was divided with the wall structure and the dielectricprotrusions. Recovery of the alignment after the display panel waspressed with a fingertip during application of 4V (white display) wasexamined. As a result, while an afterimage was hardly observed on thepressed portion (the alignment was immediately recovered) in the exampleof the present invention, an afterimage was recognized for severalminutes in the comparative example. A difference was thereforerecognized in the recovery from occurrence of an alignment disturbancewith pressing. Further, in the comparative example, it was confirmedthat part of the disturbed alignment with pressing failed to completelyrecover and caused display roughness and display failure due todefective alignment.

From the evaluation results described above, it was found that byarranging the transmission region and the reflection region alternatelyand separating the liquid crystal regions from each other with thedielectric protrusions and the wall structure, obtained were the effectof fixing or stabilizing the positions of the center axes of theaxisymmetrically aligned domains, and the effects such as reducing theroughness in grayscale display at a slanting visual angle, increasingthe response speed in grayscale display, and reducing occurrence of anafterimage with pressing. In other words, according to the LCD device ofthis embodiment of the present invention, the division structure in eachpixel can be optimized.

In the above embodiment, both the dielectric protrusions and the wallstructure were formed. The pixel region can be divided into a pluralityof sub-pixel regions as long as at least the dielectric protrusions areformed. Liquid crystal molecules tilt near the side steps of thedielectric protrusions, and this leads to division alignment of liquidcrystal molecules in the divided regions. Since the pixel region isdivided (partitioned), the division alignment can be obtained withoutexistence of a wall structure. To further stabilize the divisionalignment and improve the recovery against pressing and other featuresfurther effectively, a wall structure and openings are preferablyformed. If no wall structure is formed, openings are preferably formedin at least one of the upper and lower electrodes.

As described above, according to the present invention, an LCD devicewith excellent display quality can be implemented with a comparativelysimple construction. The present invention is suitably applied totransmissive LCD devices and transflective (transmissive/reflective) LCDdevices. In particular, transflective LCD devices are suitably used asdisplay devices for mobile equipment such as mobile phones.

While the present invention has been described with respect to preferredembodiments thereof, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many embodiments other than those specifically described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

This non-provisional application claims priority under 35 USC § 119(a)on Patent Applications No. 2004-066292 filed in Japan on Mar. 9, 2004and No. 2004-084404 filed in Japan on Mar. 23, 2004, the entire contentsof which are hereby incorporated by reference.

1-12. (canceled)
 13. A liquid crystal display device comprising a firstsubstrate having a first electrode, a second substrate having a secondelectrode opposed to the first electrode, and a vertically alignedliquid crystal layer interposed between the first electrode and thesecond electrode, each of a plurality of pixel regions being defined bythe first electrode and the second electrode, wherein at least one pixelregion among the plurality of pixel regions is divided into a pluralityof sub-pixel regions with dielectric protrusions regularly arranged onthe first substrate, and liquid crystal molecules in the liquid crystallayer in each sub-pixel region are axisymmetrically aligned around anaxis vertical to the surface of the first substrate when a predeterminedvoltage is applied between the first electrode and the second electrode.14. The device of claim 13, wherein the pixel region is surrounded witha shading region as is viewed from top, and the device further comprisesa wall structure formed to substantially surround the pixel region onthe surface of the first substrate facing the liquid crystal layer inthe shading region.
 15. The device of claim 13, wherein the firstelectrode and/or the second electrode has an opening formed in thesub-pixel region, and when the voltage is applied, the vertical axis isformed in or near the opening.
 16. The device of claim 13, wherein thepixel region is surrounded with a shading region as is viewed from top,and a support for defining the thickness of the liquid crystal layer isformed in the shading region.
 17. The device of claim 13, wherein thefirst electrode includes a transparent electrode and a reflectiveelectrode, and at least one of the plurality of sub-pixel regions is atransmission region and at least one of the sub-pixel regions is areflection region.
 18. The device of claim 17, wherein the relationship0.3 dt<dr<0.7 dt is satisfied where dt is the thickness of the liquidcrystal layer in the transmission region and dr is the thickness of theliquid crystal layer in the reflection region.
 19. The device of claim17, further comprising a transparent dielectric layer on the surface ofthe second substrate facing the liquid crystal layer.
 20. The device ofclaim 19, wherein the transparent dielectric layer has a function ofscattering light.
 21. The device of claim 17, wherein the secondsubstrate further comprises a color filter layer, and the opticaldensity of the color filter layer in the reflection region is lower thanthe optical density of the color filter layer in the transmissionregion.
 22. The device of claim 13, further comprising: a pair ofpolarizing plates placed to face each other via the first substrate andthe second substrate; and at least one biaxial optical anisotropicmedium layer placed between the first substrate and one of the pair ofpolarizing plates and/or between the second substrate and the otherpolarizing plate.
 23. The device of claim 13, further comprising: a pairof polarizing plates placed to face each other via the first substrateand the second substrate; and at least one uniaxial optical anisotropicmedium layer placed between the first substrate and one of the pair ofpolarizing plates and/or between the second substrate and the otherpolarizing plate.
 24. The device of claim 13, wherein the pixel regionis in the shape of a rectangle having a pair of longer sides and a pairof shorter sides, and is divided into the plurality of sub-pixel regionswith at least one pair of the dielectric protrusions, and the pair ofdielectric protrusions extend from near the pair of longer sides of thepixel region in the directions closer to each other and are in line witheach other in the shorter-side direction.